While it ’ s probably more effective to control plant canopy temperature through well-designed HVAC , many experienced growers have tailored their growing style to the effects of heavy IR . Understanding this concept is one of the biggest challenges for growers transitioning from HPS to LED .
FAR-RED ( 700-800nm ) — Most of the photons in the far-red range don ’ t contribute directly to photosynthesis , but combined with red photons they can increase the overall energy harvested by the plant through the Emerson Effect . Far-red light also has an important role in shade-avoidance response . When plants are exposed to high ratios of far-red light they sense they are being shaded by taller plants . In response , plants increase cell division , causing stems to stretch and leaves to expand . While these traits aren ’ t always desirable , the ability to control shade response effects could help shorten veg times and increase yields in certain cultivars . 730nm far-red diodes , which stimulate both the Emerson Effect and shadeavoidance response , are readily available and relatively inexpensive .
RED ( 600-700nm ) — Red light doesn ’ t seem to steer plant structure and development , but when it comes to biomass production , red is a rock star . The 660nm “ deep red ” is the most efficient diode currently available in terms of energy used to photons produced . It ’ s not surprising many LED grow light manufacturers pack their fixtures full of these highly efficient red diodes .
GREEN / YELLOW ( 500-600nm ) — Green is the most misunderstood color when it comes to plant lighting . Indoor cannabis growers have long known that green light can be used to illuminate grow spaces during the dark cycle without reverting their plants back to a vegetative state . That ’ s because green light doesn ’ t activate the plant ’ s light detection receptors , called phytochromes . However , as stated before , all photons in the visible light range count nearly equally toward photosynthesis , and green light is no exception . Green light plays a powerful role when it comes to canopy penetration . While red and blue photons are quickly absorbed in the upper leaf layers , many green and yellow photons pass through the leaves to be absorbed by lower growth .
RED LIGHT doesn ’ t seem to steer plant structure and development , but when it comes to biomass production , red is a rock star .”
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