Understanding PAR PPFD and PFD To Maximize Cannabis Yield

Understanding PAR, PPFD and PFD To Maximize Cannabis Yield

Professor DeBacco


Light Intensities Importance
Light intensity levels can have a significant effect on photosynthesis rates, which are directly related to a plant’s ability to grow.
Measuring the light intensity involves a few different options so it is important to know the background of each.



Lumens are for Humans
The lumen is the SI derived unit of luminous flux which is weighted according to a model of the human eye's sensitivity to various wavelengths.
Essentially it contains the wavelengths humans can easily see.
No connection to photosynthesis of plants (unlike PAR).



PAR (Photosynthetically Active Radiation)
PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis
Measured as Watts/m2
Note: Chlorophyll absorption is higher in the blue and red portions of the light spectrum, so two light sources can have the same PAR output but depending on the wavelengths produced can have different plant performances.



PPF (Photosynthetic Photon Flux)
PPF provides the number of photons in the 400-700nm wavelength range that drive photosynthesis, which are emitted by a light source, same range as PAR.
The unit of the PPF value is µmol/sec
This is the quantity of light particles emitted per second
Simply PPF = Amount per Time.
However, PPF does not consider the direction in which the light is emitted which means it does not indicate the light that actually reaches the leaves.



PPFD (Photosynthetic Photon Flux Density)
PPFD provides the number of photons in the 400-700nm wavelength range that drive photosynthesis, which are emitted by a light source, same range as PAR and PPF
The unit for PPFD is µmol/(m2s)
PPFD tells you how many photons which drive photosynthesis impact an area per second.
Simply PPFD = Amount per Area per Time



Comparing PAR vs PPF vs PPFD
PAR is a generic term still used in common speech to refer to energy flux or photon flux.
Unit: Watts/m2
PPF is used for the amount per time.
Unit: umol/sec.
PPFD is used for an amount per area per time.
Unit: umol./(m2*sec)
PPFD helps define the intensity of the light over a given area.



Limitations of PAR and PPF and PPFD
All of these are bound by the 400-700nm wavelengths of light.
However, in particular with cannabis research where the UV and Far red wavelengths are of interest these above terms do not take into account these wavelengths since they are outside of the 400-700nm range.
So to take into account greater wavelengths there is PFD



PFD (Photo Flux Density)
PFD is a measurement of the number of photons in the 300-800nm wavelength range passing through a particular area per second.
The unit is μmol/m2/sec
Simply PFD = Amount per Area per Time
Measures 300-800nm
Not limited to the 400-700nm “photosynthetic” wavelengths
Take into account the far-red and ultraviolet radiation



Units Are Important!
Always check the units used in any work you are reading!
micromoles per meter squared per second (µmol/(m2s) is key and is what PPFD is measured in.



Light Sensors
Light sensors are the primary instrument used to quantify the light intensity of horticulture lighting systems.
These sensors work by using an optical filter to create a uniform sensitivity to PAR light
Growers will use this style for a point in time measurement but some options to connect these to a data logger can allow for an accumulation of readings for different day to day comparisons.



Measuring PFD (340-1040nm)
Apogee MQ-620 Extended Range PFD Sensor allows for UV and Far-red photons to be measured.
Research has shown value of adding UV and far-red.
The 1040nm top cutoff also means the sensor will measure the thermal output of HPS fixtures and other broad-spectrum lights so, the sensor is intended only for use in LED environments.



How Can This Help To Maximize Cannabis Yield?
Since cannabis is a high light tolerant plant there are more potential options when it comes to lighting.
With the ever changing artificial lighting market, understanding these terms can help growers make informed decisions.
Also, with cannabis the secondary compounds are also of importance so providing plants with wavelengths outside of the PAR/PPFD spectrum may be advantageous when it comes to maximizing yield.

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/1dDrZ...

*Due to the description character limit the full work cited for "Understanding PAR PPFD and PFD To Maximize Cannabis Yield" can be viewed at... https://drive.google.com/file/d/1XLdm...