Daily Light Integral (DLI) Relation To Cannabis Yield

Professor DeBacco


Daily Light Integral (DLI)
Daily Light Integral (DLI) describes the number of photosynthetically active photons (in the 400700 nm or PAR range) that are delivered to a specific area over a 24hour period.
For outdoor locations this will be season and weather dependent
For indoor locations it can more easily be calculated by simply knowing the lights output and hours on.



Calculating DLI
DLI is the sum of the per second PPFD measurements during a 24hour period.
If the photosynthetic light intensity remains constant (as with artificial lighting units) for a defined time period (duration) then the DLI can be calculated.
Outdoor locations are more complicated and require more data collection over a period of time.
However, the end result is the same.



PPFD Rating Over Six Hours
PPFD in µmol/(m2sec)
Range is 02000 (no light to full sun light)
But remember that sunlight is subject to continual variability due to clouds.
For artificial lighting 510 µmol/(m2sec) should be considered the absolute minimum



PPFD vs DLI
PPFD = rate of photos per second
How fast is it raining per second?
DLI = sum of photons in a day
How much did it rain in a day? (What is the total?)



DLI Related to Stage of Cannabis
Target DLI can vary with stage of plant development.
However, if a grower is able to keep all other plant requirements at optimum the DLI can be increased above these suggested levels to maximize production



DLI Outdoor Perspective
Note on a summer full sun days DLI can reach 60 mol/m2/day
The image shows the amount of light received across the United States each month.
During fall and winter latitude has a strong influence of DLI



Converting 1000 µmol/(m2sec) for 20hr. to DLI
A plant receiving 1000 µmol/(m2sec) for 20 hours will have a DLI of how much?
Answer = 72 moles / (m2*day)
See calculations below…



Converting 1000 µmol/(m2sec) for 12hr. to DLI
A plant receiving 1000 µmol/(m2s) for 12 hours will have a DLI of how much?
Answer = 43.2 moles / (m2*day)
See calculations below…



Light Intensity Related to Cannabis Production
At a certain point in order for plants to take advantage of higher intensity lights, there needs to be CO2 supplementation
If light is increased beyond this amount the CO2 becomes the limiting factor and plants will not be able to use the extra light levels making it a waste to produce.
The Threshold for optimal growth and photosynthesis is a DLI of 65 moles per day.



Light Intensity During Veg Cannabis Phase
Since Vegetative phase can have some variability due to grower duration of light to dark the maximums are provided
Notice that if you have lights that produce less intensity they need to be run for a longer duration.
*While this is possible in Veg, the light duration is fix in flower



Light/dark schedule and PPFD recommendation without CO2 enrichment
24/0 schedule: 752.31 µmol/(m2sec) for a DLI of 65 moles / (m2*day)
18/6 schedule: 900 µmol/(m2sec) for a DLI of 58 moles / (m2*day)
Flower photoperiod comparison 12/12 schedule: 900 µmol/(m2sec) for a DLI of 39 moles / (m2*day)



Light/dark schedule and PPFD recommendation with CO2 enrichment
To reach a DLI of about 65 moles / (m2*day)…
24/0 schedule: 752 µmol/(m2sec)
18/6 schedule: 1003 µmol/(m2sec)



Flower photoperiod for comparison 12/12 schedule: 1505 µmol/(m2sec)
Light Intensity During Flowering Phase of Cannabis Production
Since the flowering phase is defined as only 12hours of continuous light the duration of light remains the same.



What is variable is the intensity which will directly impact the DLI
Minimum Level
PPFD of at least 510 µmol/(m2sec)
Optimum Range without CO2 Enrichment
PPFD of 8001000 µmol/(m2sec)
*Without CO2 max intensity that plants can use is no higher than 900 µmol/(m2sec)
Optimum Range with CO2 Enrichment
PPFD of 10001500+ µmol/(m2sec)
Does not seem to be a saturation point even up to 1800 µmol/(m2sec)


Special Thanks To…
Combination of research data from…
Dr. Bruce Bugbee of Utah State University and Founder of Apogee Instruments Inc.
Shane Torpey MICRO founder

Professor Erik Runkle of Michigan State University


Link to Lecture Slides: https://drive.google.com/file/d/1LCG4...

*Due to the description character limit the full work cited for "Daily Light Integral DLI Relation To Cannabis Yield" can be viewed at... https://drive.google.com/file/d/1ygpD...