MJBizMagazine September 2021 Lighting Buyers Guide - 9

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Higginbotham agrees.
" You can be incredibly efficient with LEDs when they apply only blue and red, and surprisingly, those are
very efficient wavelengths for the plants, " Higginbotham said.
" I do support blue and red light in a greenhouse situation because we already have full spectrum. LEDs give
you that option, and that influences the cost. "
LOCATION AND CLIMATE AFFECT GREENHOUSE LIGHTING NEEDS
Where a greenhouse is located and prevailing weather patterns make a significant difference in lighting
requirements.
Marc van Iersel, horticulture professor at the University of Georgia and co-founder with Mattos of the lighting
technology consulting firm Candidus, recommends studying daily light integral maps to calculate day
length. He also recommends taking measurements both outside and inside your greenhouse.
Redefining PAR Could Improve LED Efficacy
Since the 1970s, horticultural lights have
used a definition of light wavebands
that plants are known to respond to
photosynthetically.
But the definition, known as
photosynthetically active radiation, or
PAR, is incomplete, resulting in limits on
the efficacy of LED fixtures, says Marc
van Iersel, horticulture professor at the
University of Georgia.
PAR was defined in the 1970s as wavebands
in the light spectrum between 400 and 700
nanometers (nm) by scientists measuring
how plants responded to individual
wavebands of light, van Iersel said.
However, scientists have long known that
plants do use wavebands outside the PAR
definition, including far-red light, which is
between 700 nm and 850 nm.
" Research from the 1950s found that if you
combine PAR with far-red light, then farred
light is photosynthetically active, " van
Iersel said.
" That has been known for 70 years now, but
people for whatever reason have forgotten
about it. "
As a result, the current light-efficacy
testing guidelines don't count the photons
produced by far-red light. But they do
include the extra energy to produce those
photons. That makes " lights look worse
based on how the testing is done, " van
Iersel said.
But the real issue is that far-red light is the
most energy-efficient waveband that LED
fixtures can emit, van Iersel said.
" If we started counting far-red light as
well... it would actually increase the efficacy
(rating) of LEDs, " he said.
Light manufacturers may choose not to
include far-red light because they are
penalized under current testing protocols
unless PAR is redefined. This is despite the
fact that it actually makes their lights more
efficient, according to van Iersel.
Some lights may not qualify for rebate
programs, another disincentive to including
far-red.
" The standards of how light fixtures are
assessed really needs to reflect the latest
science, and right now, they don't, " van
Iersel said.
9
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MJBizMagazine September 2021 Lighting Buyers Guide

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