grow cycle | tips and tricks
Why Humans Use Lumens and Plants Use PAR
Humans need light to perceive color and brightness while plants need light to support photosynthesis . Using the correct metrics and instruments to calculate PAR is essential to avoid adverse lighting effects on your crop .
by Josh Gerovac
Whether you are using horticulture lighting systems to provide supplemental lighting in a greenhouse or sole-source lighting indoors , it is important that you know the quality and quantity of light that your fixtures are providing to your plants . There are numerous metrics used to measure light ; however , certain ones were developed for applications related to human vision , while others were developed specifically for measuring light that influences plant growth and development .
Humans use Lumens
It goes without saying that plants perceive light very differently than humans . Where plants use light to drive photosynthesis and other light-mediated physiological responses , humans and many other animals use something called photopic vision in well-lit conditions to perceive color and brightness of light . Lumen is a
“ Humans may not be efficient at perceiving light in these regions , but plants are highly efficient at using blue and red light to drive photosynthesis .” unit of measurement based on a model of human eye sensitivity in well-lit conditions , which is why the model is called the photopic response curve ( Figure 1 ). As it shows , the photopic response curve is bell-shaped and shows how humans are much more sensitive to green light than blue or red light . LUX and foot candle meters measure the intensity of light ( using lumens ) for commercial and residential lighting applications , with the only difference between the two being the unit of area they measure ( LUX uses lumen per square meter and foot candle uses lumen per square foot ). The fundamental problem with using LUX or foot candle meters when measuring the light intensity of horticulture lighting systems is the underrepresentation of blue ( 400 – 500 nanometers ) and red ( 600 – 700 nm ) light in the measurement . Humans may not be efficient at perceiving light in these regions , but plants are highly efficient at using blue and red light to drive photosynthesis .
Plants use PAR
Plants primarily use wavelengths of light between 400-700 nm to drive photosynthesis ( Figure 1 ), which is why this range is called photosynthetically active radiation ( PAR ). PAR is a much-used ( and often misused ) term related to horticulture lighting . PAR is not a measurement or metric like feet , inches , or kilos . Rather , it defines the type of
80 Maximum Yield USA | February 2017