65 DLI and lighting schedules

[RastaDaddy]

I will ask this question on some subreddits and forums I trust. Since we know that cannabis needs a DLI of 65, we can assume that the plant can take this in a maximum of 24 hours or in a minimum of 8-9 hours(maybe even less than that, but currently we don't have the technology to give that much light).

In a 24-hour lighting schedule, the PPFD should be around 750 to achieve 65 DLI. For 9 hours of lighting at 65 DLI, the PPFD should be 2000. So, has this been tested? Can the plant use the energy created in 9 hours as well as schedules with more than 12 hours of lighting? If this particular case has a research paper about it, please share it with me. I know that it has been tested that cannabis yields almost 1:1 with a linear increase in light up to 1,800 PPFD, and that started to diminish from 1,800 to 2,500. While yield increased up to 2,500 PPFD, it was more bell-shaped than linear beyond 1,800 PPFD.* Since almost all plants are adjusted to take in whatever they can the sun gives them(2000 PPFD is summer noon sun), I don't see why we can't implement a 9-hour lighting strategy paired with a low-wattage CFL before and after the schedule to prevent flowering.

This way, people living off-grid(or on-grid with PV panels) should be able to give their plants what they need 24/7, 365 days a week, almost anywhere on earth, with their PV solar energy panels, and they won't have to buy really expensive batteries to keep lighting them in the night. So, what are your thoughts on this?


*Rodriguez-Morrison V, Llewellyn D, Zheng Y. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Front Plant Sci. 2021 May 11;12:646020. doi: 10.3389/fpls.2021.646020. PMID: 34046049; PMCID: PMC8144505.

 

[Son of Hobbes]

Since we know that cannabis needs a DLI of 65, we can assume that the plant can take this in a maximum of 24 hours or in a minimum of 8-9 hours(maybe even less than that, but currently we don't have the technology to give that much light).

Who says cannabis needs DLI of 65? That should be our first question in this investigation.

 

[Son of Hobbes]

In a 24-hour lighting schedule, the PPFD should be around 750 to achieve 65 DLI. For 9 hours of lighting at 65 DLI, the PPFD should be 2000. So, has this been tested? Can the plant use the energy created in 9 hours as well as schedules with more than 12 hours of lighting? If this particular case has a research paper about it, please share it with me. I know that it has been tested that cannabis yields almost 1:1 with a linear increase in light up to 1,800 PPFD, and that started to diminish from 1,800 to 2,500. While yield increased up to 2,500 PPFD, it was more bell-shaped than linear beyond 1,800 PPFD.* Since almost all plants are adjusted to take in whatever they can the sun gives them(2000 PPFD is summer noon sun), I don't see why we can't implement a 9-hour lighting strategy paired with a low-wattage CFL before and after the schedule to prevent flowering.

DLI isn't a magic dial that by cranking it up, it "just" automatically increase your yields. It's not that simple.

Since almost all plants are adjusted to take in whatever they can the sun gives them(2000 PPFD is summer noon sun),

This is a false statement . Most plants actually do NOT do this.

DLI is increased by either increasing the amount of available light hours to the plant, or increasing the light intensity available to the plant.

While photosynthetic rates increase with increased light intensity, photosynthesis quickly becomes "light limited" based on other environmental factors, generally CO2 and temperature. That means that at a certain saturation point, you can hammer your plants with as many photons as you can provide, but the plant is only going to use what it can use, and the rest is either wasted or now potentially damaging the plant (this is what's called "photoinhibition.")

So to increase DLI to any real benefit/gain, you -have- to address your other environmental variables!

When plants are exposed to more light energy than they can process into sugars, that extra energy has to go somewhere. Excess light produces what are called "reactive oxygen species (ROS)" in plants by overwhelming the photosynthetic electron transport chain in the chloroplasts, causing electrons to "leak" and react with oxygen. The light energy excites chlorophyll but the energy isn't used for photosynthesis, eventually leading to cell damage, or photooxidation (which shows up as pale or burnt leaves.)

Then we would want to address canopy management (we had a good discussion about defoliation the other day and how light penetration factors in.) Not to mention to achieve those high levels of PPFD, how close you'd have to be to the canopy, or the heat generated by a light (or lights) capable of producing this type of intensity.

Unless you are running an incredibly dialed in space, compressing DLI into a shorter, very intense day is not automatically better (and will likely lower efficiency and increase stress.)

A better goal with would be to maximize usable light, not raw DLI.

 

[Lil Dab]

 

[Frankthetank]

Who says cannabis needs DLI of 65? That should be our first question in this investigation.

Autos are only recommended at 55 dli with co2…otherwise it’s 45.. 65 will cause light stress issues. Believe me