Maximum Yield Cannabis Canada 2017 July/August | Page 54

leaf surface temperature
OPTIMIZING GROWTH UNDER LED GROW LIGHTS
When growing under LED lights with a red- and blue-domi-
nant plant-optimized spectrum, the lack of excess infrared and
other directly-usable light causes the leaves to remain cooler,
meaning that ambient air temperature needs to be signifi-
cantly warmer than for the same plant grown under any light
(natural or artificial) that is not optimized for plant growth.
LED lights utilizing primarily “white” LEDs, which are
actually optimized for human eyes, are dominated by mostly
yellow and green light output. This lack of plant efficiency will
warm up leaves more than a red- and blue-dominant spectrum,
but because they still lack the 800+ nm infrared output of most
HID lights, the ambient air temperature may still need to be a
little warmer to get the ideal LST.
If you are switching from traditional HID lighting to LED,
you can turn the temperature up a bit with white LEDs, but
you need to turn it up more if you are using a plant-tuned
spectrum. Not adjusting ambient air temperature to account
for the spectrum change can limit your plants’ growth, and
ultimately your yields.
COMPARING LED GROW LIGHTS TO OTHER
GROW LIGHTING TECHNOLOGIES
When growing with plant-optimized LED lights, it is important
to realize that ambient air temperatures need to be kept
higher compared to other lighting to achieve the same
metabolic rate. Side-by-side tests of LED lights versus other
lighting such as HPS, where ambient air temperature is kept
the same, are not particularly informative or accurate as to
the lights’ relative performance—the tests should be run so
that leaf surface temperature is being kept the same under
each light to enable identical metabolic rates. As the data
from FLIR camera observations shows, this becomes more
critical especially when comparing plant-optimized LED
grow lights to MH and HPS, as the leaf surface temperature
difference is much higher with these lights.
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grow cycle
“NOT ADJUSTING AMBIENT air
temperature to account for the spectrum
change can limit your plants’ growth, and
ultimately your yields.”
RELATIVE ENERGY SAVINGS
Heat mitigation is required in most indoor gardens using
artificial lights, whether it is achieved with ventilation
or air conditioning. Plant-optimized LED grow lights can
offer substantial energy and cost savings in cooling.
LED lights already contribute less heat to the growing
environment than HPS, metal halide (MH), and fluorescent
lights due to higher efficiency of light generation. Running
a warmer indoor garden, as required for LED with a plant-
tuned spectrum, can lead to a profound reduction of costs
associated with cooling—not just running the cooling
equipment, but also in sizing it as well.
Even growing areas currently relying on excess heat
from conventional grow lights can easily reduce costs
with plant-optimized spectrum grow lights. In most indoor
grow areas, something as simple as plastic sheeting can
provide sufficient additional insulation to avoid the need
for other forms of heat. In greenhouses, natural gas or
propane heaters are usually much more cost-effective than
relying on electric lights for heat.
If growroom cooling is achieved partially or entirely through
ventilation, and CO 2 supplementation is being used, the
reduced need for cooling when using LED plant lights will
also result in less loss of CO 2 further increasing savings.
Every grower knows how important it is to keep your plants
happy at the right temperature for maximum yield. LED
technology allows better control of the light spectrum than
ever before, and this translates into cooler leaves for your
plants at the same ambient temperature. Unless you raise the
air temperature with plant-optimized LED grow lights, you are
keeping your plants too cool, harming your yields, and costing
you more in unnecessary cooling. With non-plant-optimized
“white” LEDs designed for human eyes, you may still need to
raise the temperature a few degrees, but not as much as with
red- and blue-dominant, plant-optimized LED grow lights.