the right light for vegetative growth
The largest disadvantage of LEDs is
their price. Although an increasing
amount of LED manufacturers continues to bring the price down, LEDs
are still more expensive than other
commonly used lighting technologies. When purchasing LED fixtures,
a grower is making a long-term investment. LED fixtures will eventually pay
for themselves with the savings accrued
from not having to replace the bulbs
and the reduced heat loads.
Induction Lighting
Most recently, two types of induction
lighting have entered the indoor
gardening market: induction fluorescents and sulfur plasma. Both of
these lighting technologies can be
used for vegetative growth with good
results. Induction fluorescents have
similar qualities to T5 fluorescents,
but their spectral output will not
degrade over time. In many ways,
induction fluorescents are the perfect
vegetative light: they produce uniform light energy over the span of
the fixture, have a low heat signature
and last for 15 years. As with LEDs,
the biggest disadvantage with induction lighting fixtures is their initial
cost, but for committed growers, they
are worth considering.
Sulfur plasma lighting is the
most recent horticultural lighting
technology to emerge. Sulfur
plasma lighting has an incredible
spectral output—closer to that of
the sun than any other lighting
technology—making it an ideal
candidate for both vegetative and
flowering stages. As this technology
is developed more for horticultural
purposes, it is plausible that sulfur
plasma lighting will eventually
become the standard light source for
indoor horticulture. Like LEDs and
induction fluorescents, sulfur plasma
lights last for 10-15 years without
significant depreciation of usable
light energy. The initial cost for
sulfur plasmas is still high, but over a
long period of time, the advantages
of this technology can make the
initial investment worthwhile.
Vegetative Lighting
Techniques
Regardless of the type of lighting
technology one chooses for vegetative growth, there are a few general
rules of thumb that will help growers maximize their growroom’s light
energy. First of all, always keep the
light source as close as possible to the
plant canopy. For vegetative growth,
increased light energy equates to
tighter node spacing and more robust
stalks, depending on the crop. In
some cases, especially when growing
a wide variety of plants, a grower may
need to use manipulation to keep
a plant canopy uniform. Topping,
pruning, super cropping, tying down
and trellising are all methods growers
can use to keep the plant canopy as
uniform as possible.
During vegetative growth, the lights
should be on 18-24 hours a day.
Although many growers will insist
a 24-hour light cycle will speed up
growth, I have always preferred an
18-hour light cycle. I believe plants,
“When purchasing LED fixtures, a grower is making a long-term
investment. LED fixtures will eventually pay for themselves with the savings
accrued from not having to replace the bulbs and the reduced heat loads.”
54
Maximum Yield USA | April 2015