What is PAR?
PAR stands for Photosynthetically Active Radiation. PAR covers the spectral range of solar radiation between 400-700 nanometers. The lower end of this range (400) is called the blue spectrum, which is best for vegetative growth. The high end of this range (700), called the red spectrum, is best for flowering growth. Light within the PAR spectrums is what plant growth needs the most. On the other hand, lights below the PAR range are ultraviolet, x rays, and gamma rays; above the PAR range are infrared and radio waves.
Are Lumens the same as PAR?
Lumens are the measurement of light output visible to the human eye. It tells the human eye how bright a bulb is. But it does not mean that a brighter light means better growth for plants. Light needs to be in the right PAR color spectrum for it to be most beneficial for plant growth.
What does PPF mean?
While PAR defines the spectrum of lights, PPF (Photosynthetic Photon Flux) measures the PAR light produces per second -- expressed in micromoles per second (μmol/s). The higher the measurement, the more effective the light can be for plants. In other words, the more light the plant can use, the better it’s photosynthesis. That translates into higher quality plants. However PPF does not tell us how much of the actual light is received by the plant, which brings us to the next topic - PPFD.
What does PPFD mean?
PPFD (Photosynthetic Photon Flux Density) measures the actual amount of light received on each plant. More specifically defined by scientists is, "the number of photosynthetically active photons that fall on a given surface each second". It is a measurement of a specific location on your plant, measured in micromoles per square meter per second (μmol/m2/s).
What does DLI mean?
The last measurement that you should understand is DLI (Day Light Integral). DLI measures the total amount of light delivered to a plant per day. Whereas PPFD is a measurement per second, DLI is per day (or duration of the photoperiod determined by the cultivator). Scientifically speaking, it is the accumulation of of moles of photons per square meter per day expressed as (mol/m2/d). You can calculate DLI with the following formula:
[PPFD x (3600 seconds/hour x number of hours during photoperiod)] / 1,000,000 (μmols/mol) = DLI (mol/m2/d).
Growers can use DLI to monitor the daily light received on the plants, thereby determining whether they need supplemental lighting to increase DLI or make adjustments to decrease the DLI for plants.