“ Understanding the correct metrics to use will not only allow
horticultural LED lighting
“ Understanding the correct metrics to use will not only allow
you to make better purchasing decisions of horticulture lighting systems , but will ultimately make you a better grower . ”
Photosynthetic photon flux is a very important metric if you want to be able to calculate how efficient a light is at converting electrical energy into photons of PAR . If the PPF of the light is known along with the input wattage , you can calculate how efficient a horticulture lighting system is at converting electrical energy into PAR . However , it is important to note that PPF does not tell you how much of the measured light actually arrives to the plant canopy . While it ’ s nice to know the PPF of a lighting system , PPF alone is often useless information to a grower .
Photosynthetic Photon Flux Density
Photosynthetic photon flux density ( PPFD ) measures the amount of PAR that actually arrives at the plant , or , as a scientist might say , “ the number of photosynthetically active photons that fall on a given surface each second .” PPFD is a ‘ spot ’ measurement of a specific location on your plant canopy , and it is measured in micromoles per square meter per second ( μmol / m 2 / s ). If you want to find out the true light intensity of a fixture over a designated growing area , it is important that the average of several PPFD measurements at a defined height ( typically , the top of your crop canopy ) are taken . Lighting companies that only publish the center point PPFD directly below their lighting fixture grossly overestimate the true light intensity of a fixture . A single measurement does not tell you much , since horticulture lights are generally brightest in the center , with light levels decreasing as measurements are taken towards the edges of a coverage area . It is easy for lighting manufacturers to manipulate PPFD data if buyers are not educated on the proper way to measure PPFD . To ensure you are getting accurate PPFD values over a defined growing area , the following needs to be published by the manufacturer : the maximum , minimum , and average measurement ; measurement distance from light source ( vertical and horizontal ); number and location of measurements ; and the min / max ratio if only an average PPFD is provided .
“ PPF ” is commonly used to describe PPFD by academics in peer-reviewed journals , and debate continues among plant scientists and engineers on which usage of the term is correct . One way to avoid ambiguity when reading a journal article or product brochure is to focus on the unit of measurement . If the unit includes m 2 , then the unit is referring to the light intensity at the surface of a plant canopy ( PPFD ). If m 2 is not included , then the unit is referring to the total PAR emitted from a light source ( PPF ). Understanding the correct metrics to use will not only allow you to make better purchasing decisions of horticulture lighting systems , but will ultimately make you a better grower .
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