Page 12 - Griffin Gazette Fall 2015

Light Well, Grow Well:
By Tami Van Gaal, GGSPro Technical Specialist
Supplemental lighting needs for
greenhouse crops generally fall into
two buckets: 1) increasing light
intensity to improve growth and quality
and 2) manipulating photoperiod for
control of flowering. Fortunately for
most finished growers, the need for
supplemental lighting for spring crops
is limited to the easier, less expensive January in a northern state. A bench level DLI of 3 mol/m2/d
photoperiod bucket. Even for growers
in the northern tier of states, the
need to increase light intensity is generally restricted to the
earliest weeks of the spring production cycle. The need for
increased light intensity can change dramatically, however,
when a grower chooses to propagate young plants earlier in
the season.
The timeline for young plant propagation precedes typical
spring production dates by 6-12 weeks (crop dependent),
such that plug crops are in production during January and
February, months with notoriously short days and low light
levels. For many growers, this means that ambient light
conditions are not adequate to produce a well-branched, well-
toned crop. Lighting propagation areas should be considered
a requirement for most growers during this timeframe, not
an option.
Lighting production spaces costs money, and nobody
wants to spend money needlessly. Therefore, it's important
to understand when to provide supplemental lighting, how
to determine how much light is needed, and which fixtures
provide the best solution. When we describe the amount of
light that should be delivered to a crop over the course of
a day, we are talking about a cumulative daily light integral
(DLI). Accepted DLI targets for young plant production (from
seeds or cuttings) range from 8-12 mol/m2/d at crop height
(N. Mattson, Cornell University). To produce a quality crop,
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Lighting
Young Plants
propagation from both seeds and cuttings should occur
under no less than 8 mol/m2/d. While ambient, outdoor light
levels generally exceed 10 mol/m2/d in January and February
for all but the most northern growers (J. Faust, Clemson
University), a significant portion of this light (40-70%) is
blocked by poly and structures during this same time (N.
Mattson, Cornell University). Some quick mental math reveals
that DLIs in the range of 3-6 mol/m2/d can be expected in
would require an additional 5 mol/m2/d from supplemental
lighting to reach the minimum level of 8 mol/m2/d.
Because so much light can be blocked by structures, DLI
should be measured at crop level and not assumed based
on outdoor, ambient light. A LightScout from Spectrum
Technologies (sold by Griffin) tracks DLI for a single day in
a simple-to-use, easy-to-place device. For growers wanting
longer data collection periods, the Watchdog WeatherTracker
(also from Spectrum Technologies) provides additional logging
features in a larger format. Using the data you collect from your
greenhouse, the Griffin Construction team can work with you
to develop the perfect lighting solution. Options for increasing
DLI in the greenhouse include the following types of lights:
High-Intensity Discharge (HID) lamps – Available with high
pressure sodium (HPS) or metal halide (MH) bulbs, the newest
HID lighting systems are designed for maximum output with
a compact fixture to minimize shading. Greenhouse fixtures
are much smaller than their warehouse counterparts. Fixtures
are available in wattage ranging from 250-1000 W, which
means the system can be tailored to your needs. New fixtures
and ballasts are far more efficient than older models, with
a cost of operation that can be comparable to some LED
solutions (Nelson and Bugbee, Utah State University).
Light-Emitting Diode (LED) lamps – LEDs are garnering
much attention in our industry, with rapidly expanding and
evolving product options from numerous manufacturers. The