Hydrolife Magazine April/May 2017 (Canada Edition)

grow
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 metre per second (µmol/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 unfavourable growth and
development. This is why lumens, LUX,
and foot candles should not be used as
metrics for horticulture lighting.
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 sole-source LEDs on growth,
morphology, and nutrient content of
edible, ornamental, and medicinal crop
production. He has a BSc in horticulture
production and marketing, and a MSc in
horticulture, both from Purdue University.
Figure 2
Using a quantum meter to measure light intensity.
22 grow. heal. live. enjoy.
myhydrolife.ca