light needed to support photosynthesis . The amount and spectral light quality of PAR are the important metrics to focus on . Quantum sensors are the primary instrument used to quantify the light intensity of horticulture lighting systems . A quantum sensor measures the total amount of PAR landing on a specific location of your plant canopy and is measured in micromoles per square meter per second (ยต mol / m 2 / s ). These sensors work by using an optical filter to create a uniform sensitivity to PAR light , and can be used in combination with a light meter to measure instantaneous light intensity or a data logger to measure cumulative light intensity ( Figure 2 ). If you used a LUX or foot candle meter to measure the intensity of a horticulture lighting system , you would end up receiving different values depending on the spectrum of the fixture , even if the fixtures were providing the same PAR intensity to your crop . For example , if you took a measurement using a LUX or foot candle meter under a fixture using broad spectrum ( i . e . white ) light emitting diodes ( LEDs ), you would receive a much higher value than if you took the same measurement under a fixture with red and blue LEDs , even if both fixtures were providing the same amount of PAR . This will cause growers to miscalculate the actual amount of PAR they are delivering to their crop , which can lead to unfavorable growth and development . This is why lumens , LUX , and foot candles should not be used as metrics for horticulture lighting .
Figure 2 . Using a quantum meter to measure light intensity .
When you are looking to optimize growing conditions by measuring and fine-tuning light intensity in a controlled environment , it is extremely important to use the correct metrics and instruments . The amount of PAR delivered to a crop has a direct correlation to the amount of water , CO 2 , and nutrients a plant requires , in addition to other environmental factors ( e . g . temperature and humidity ) that need to be adjusted based on light intensity . Measuring lumens instead of PAR is just one example of using incorrect metrics for horticulture lighting that can have an adverse effect on your crop .
Josh Gerovac is a horticulture scientist at Fluence Bioengineering . He has spent the last decade working in controlled environment agriculture , ranging from growth chambers to commercial greenhouses . His research and practice is focused on the influence of light intensity and spectral light quality from solesource LEDs on growth , morphology , and nutrient content of edible , ornamental , and medicinal crop production . He has a Bachelor of Science in Horticulture Production and Marketing , and a Master of Science in Horticulture , both from Purdue University .
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Figure 1 . Graph depicting the average photosynthetic efficiency of plants and the spectral range that photosynthetically active radiation ( PAR ) and lumens are measured .
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