Maximum Yield Australia/New Zealand March/April 2018 | Page 46

understanding different grow lights
LEDs
Light emitting diodes (LEDs) have become the grow
light of choice for many professional and hobbyist
growers alike. These products can emit light in
wavelengths ranging from 250 nm to more than 1,000
nm. Most plants require wavelengths of light ranging
from the blue section of the spectrum at about 450 nm
to the far-red end of the spectrum at about 730 nm at
different times of their development. Light emitting
diodes have the capability of having their spectra
manipulated to efficiently capture the nuances of the
emitted wavelengths.
These lights are also favoured because of their long
life and efficiency. They have been shown to last more
than 50,000 hours, with efficiency usually ranging from
a low of 38 per cent to a high of more than 50 per cent.
They are also extremely useful for growers because
some LED lights can emit light in specific ranges of
wavelengths to support plants during their vegeta-
tive and blooming phases. Light emitting diodes do not
require the addition of any kind of reflector, as the light
is directly emitted towards the plants and not dispersed
like other types of grow lights.
A 2014 study conducted by researchers at Purdue
University showed that LED lighting was more
effective for development of commercially viable
bedding plants than HPS lighting. This study included
popular annuals such as geraniums, impatiens,
petunias, salvia, and others.
The main obstacle for growers is the relative high cost
of LEDs. The cost of LEDs, however, is dropping as they
continue to be produced in higher volumes by more
manufacturers. A current study released this year in
the journal HortScience cites that it still costs five to 10
times as much to set up a new LED grow light system as
compared to a new HPS system.
Another drawback of LED lighting is one of its
selling points. Because far less light is lost or
scattered with LED beams, it is not necessarily the
best choice of lighting for larger operations. These
lights can be thought of as more surgical, while
HID lighting is designed for saturation. Small grow
operations will likely see more benefit with a switch
to LEDs than their larger counterparts.
Sulphur Plasma
Sulphur plasma lights are the new kid on the block in
the world of grow lights. Their high cost will keep them
out of the hands of the casual grower for a while until
market factors kick in based on their effectiveness for
supporting plant growth. Many units currently sell for
thousands of dollars each.
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grow cycle
“ LIGHT EMITTING diodes have
the capability of having their spectra
manipulated to efficiently capture the
nuances of the emitted wavelengths.”
The amount of peer-reviewed literature on this
new technology useful for the layman is scant, so
it is difficult to glean an unbiased review of their
performance. Of all the possible options in grow
lights, the sulphur plasma light is touted to emit light
in frequencies and wavelengths closest to that of
the sun. It is the only grow light that emits lights via
microwaves. Its efficiency has been reported by some
European researchers as high as 70 per cent.
Final Considerations
Don’t forget about the inverse-square rule when placing
your grow lights. The amount of light that is scattered
or lost grows exponentially larger the higher the lights
are suspended over the crops. Every time you double
the distance between your light source and your plants,
they receive one-fourth of the amount of light than when
you started. This is important when considering a type
of grow light that produces a lot of heat, which needs to
be kept away from crops to avoid burning of foliage.
Ultimately, whichever light is chosen for optimal
growth, remember that all plants still need a daily
period of darkness to complete their normal cycles.
The amount of darkness a plant experiences provides
cues to the plant regarding when to flower or when to
produce vegetative growth (photoperiodism).