Understanding Light Intensity to Drive Cannabis Production

Understanding Light Intensity to Drive Cannabis Production

Professor DeBacco


Giving the Plant More Light…
When you give a plant more light this can theoretically increase photosynthesis and result in more biomass.
However, no other factors can be limiting for this to occur
(Ex. Water, nutrients, air,…)
Increasing PPFD past 850-900 µmol/(m2sec) will require carbon dioxide enrichment to take advantage of this level of light.



Light Intensity by Strain…
All Cannabis can be treated as high light intensity tolerant since all have been bred outside for an extended period of time during the history of the plants domestication process.



Growers Typically Increase PPFD as Plant Ages
While some growers increase light intensity with age, if the plant requirements are kept optimum plants can be grown at a high consistent PPFD.
This can be a challenge with water especially when plants (and root systems) are small.



Net Photosynthesis and Transpiration While Increasing PPFD
Photosynthetic response of cannabis
Variations in net photosynthesis in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions expressed in Celcius.



Light Intensity Maximum
With no Carbon dioxide enrichment the maximum PPFD that the plants can utilize is 900 µmol/(m2sec)
For plants to use light levels over this CO2 needs to be added to the growing environment.



PPFD Level Determined by [CO2]
Since CO2 concentration will be the limiting factor the level of CO2 in a grow space determines the maximum PPFD the plants can use.
*Assuming all other factors are not limiting.
(Ex. Water, nutrients,…)



Light Intensity At Both Extremes
While growers focus on the maximum light intensity to get the greatest yield for photoperiod dependent strains it is also important to consider the other end of the spectrum.

While it can be difficult to measure very low light levels (without special sensitive equipment) it is also important to consider how dark the dark period needs to be.



How Dark Should the Dark Period Be?
Many growers will ensure there is not a pin hole size of potential light entering the plants during their dark phase, this may be unnecessary.
Full moon light will not impact cannabis (light sensitive at night, just like poinsettias)
However, it may not take much more light exposure than a full moon to have the plants consider it to be “day”.

So just realize dark does not have to be 100% no light




Link to Lecture Slides: https://drive.google.com/file/d/1e9hr...

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Growers Typically Increase PPFD as Plant Ages
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