A Girl with a Bad Reputation
Up until the late 1800s, and for years after, the tomato was
considered poisonous by the majority of people across the
world. In Europe, for example, the upper crust of society ate
from plates containing lead. The highly acidic juice from the
tomato would leach lead from the plate and, as a result, a high
number of people died from lead poisoning. Naturally, they
blamed the tomato.
Being botanically classified in the deadly Nightshade family
didn’t do much to instill consumer confidence, either. Once
confirmed they were not poisonous but delicious and so culi-
nary friendly, the love affair with the tomato began in earnest.
Tomatoes have become one of the most popular vegetables
(technically a fruit) in the world and grown in some 85 per cent
of outdoor gardens.
Growing tomatoes indoors, however, is another matter.
LED There be Light
The Trouble
with Growing
Tomatoes
Indoors
Using LEDs
by Alan Ray
Anyone who ever found themselves while
losing themselves in a tomato garden
knows truer words were never spoken.
Unfortunately, growing tomatoes indoors
with LED lights isn’t therapeutic at all.
To better understand the relationship between growing toma-
toes indoors and light emitting diode (LED) lights, I sought the
expertise and wisdom of lighting maven and researcher Carey
Mitchell, professor of horticulture at Purdue University in West
Lafayette, IN. The good professor was kind enough to cram
me into his hectic schedule between his teleconference with
NASA and grading finals.
Professor Mitchell has spent years experimenting with LED
lights and their viability as an alternative light source to high
intensity discharge (HID) lights. These include metal halide
(MH) and the high-pressure sodium (HPS) lamps used in
commercial indoor growing.
I explained to the professor the article I was writing involved
growing tomatoes indoors for the home gardener using LEDs.
His first words were: “Well, they’re going to have a hard time
doing that. Tomatoes are a high-light species and you’d have
to put all the LED lights in the world to those. That’s why the
commercial hydroponic tomato production industry is green-
house-based. They merely use electric lighting to supplement
sunlight, especially in times of the year when the photoperiod
is very short or it’s very cloudy or it’s snowing. Additionally,
98-99 per cent of that market is high pressure sodium lighting
because it costs so much less to get into that initially.”
Mitchell went on to say LEDs are so expensive to begin with
that it is still cheaper to use HPS lighting, despite the fact they
cost 75 per cent more to operate. He also noted HPS lights help
heat the greenhouse. I chimed in that seems like an expen-
sive way to heat a greenhouse. The professor agreed, but also
noted heat was one of the perks of using HPS lights. He stated
their initial fixture costs are so much less than LEDs and that
they get “good stimulation of yield,” so it is still more econom-
ically feasible. Moreover, the residual radiant heat is used to
offset the enormous cost of heating a greenhouse with natural
gas or additional electricity when the photo period is very
short or during cold or cloudy periods.
LED Advantages
LED lights are becoming more efficient as their ability to
economically convert electricity into photons increases.
While currently somewhat low, they are getting better at
it. According to Mitchell there are advantages that LEDs
hold over other light sources. He said the secret is they emit
practically no heat and can thereby be placed much closer
to the plants without scorching them, which results in
reduced electrical costs.
One drawback to using LEDs in a greenhouse is they can
block out the natural sunlight from the glass panels, so it
becomes a trade-off as to when the benefit of their light is
overshadowed by the sunlight they block out.
Maximum Yield
45