Seed Germination Using LEDs

By Johann Buck
and David Kuack
Light along with
water, oxygen and temperature are the environmental factors that affect seed
germination. Light can stimulate or inhibit seed germination or have no affect
at all. Some of the plants that require light for germination include:
ageratum, begonia, browallia, coleus, geranium, impatiens, lettuce, nicotiana,
petunia and snapdragon.
Many growers who
provide supplemental light for seed germination have used fluorescent lamp
fixtures. These lamps are typically suspended 6 to 12 inches above the seed
trays. The lights are generally operated for 14 to 16 hours a day.
Some growers who
operate more elaborate production facilities have installed high intensity
discharge (HID) lamps. These lamps can be used to provide supplemental light
for both germination and growing on a crop especially during dark weather
periods and the shorter days of the year.
Consider LEDs
The light
emitting diode (LED) is gaining interest among growers and other
horticultural-related companies, including breeders and plant propagators. LEDs
are more like computer chips than light bulbs because they are solid-state
semiconductor devices.
LEDs are more
efficient than incandescent and fluorescent lamps and comparable to HID lamps.
Unlike these traditional lamps, LEDs generally do not burn out. The life
expectancy of LEDs is based on the time (in hours) required for the light
output to drop below a percentage of the original maximum intensity under
optimal operating conditions.
Growers generally
replace their lamps when the light output drops below 90 percent. Those who
install LEDs can expect a long operating lifetime of approximately 25,000 to 50,000
hours. The LEDs’ long operational life reduces the costs associated with
replacement, disposal and labor. LEDs turn on and off instantly and do not
require warm-up time like HID lamps. LEDs also emit little or no radiant heat
enabling them to be placed closer to the plants. This allows growers to produce
multilayer crops without having to be concerned about having to remove excess


Improved light efficiency
Most plants use
light in the blue (450 nanometers) and red (660 nanometers) wavelengths of
photosynthetically active radiation for photosynthesis. LEDs designed for use
in horticultural applications emit light in the red or blue wavelengths. In
some cases far red light is needed by the plant and can be added to the overall
LED light recipe.
Changing the
light recipe enables growers to manipulate the light quality to specifically
match the plant species and stage of production. LEDs give growers the option
of changing the light quality to match what they are trying to accomplish with
a crop, be it speed up growth to reduce crop time, hasten and/or increase flowering,
improve plant quality, grow without daylight or increase plant production with
a multilayer cropping system.
Multilayer production systems
Both hobbyists
and professional growers have expressed an interest in using LEDs during seed
germination. For professional growers, a multilayer production system can be a
costly and time-consuming design and construction project. Because of these
issues, smaller growers believe that LED technology is unattainable. This is
not the case.
Many large
growers start with LEDs by conducting small scale trials. These trials are
comparable to what hobbyists or smaller growers would need to satisfy their
entire crop.
An example is the
Philips GreenPower LED Production Module. It is designed to replace fluorescent
lamp fixtures. The Production Modules are available in two lengths (4 and 5
feet). The Production Modules provide either a combination of deep red and blue
light or deep red and white light. The white light is useful for color
recognition of plants and is easier on the human eye. Most growers choose the
deep red and blue light Production Module because its price point is lower than
the deep red and white light module.
For most purposes one Production Module can replace two fluorescent tube lamps. For
example, growers commonly use a plant production footprint of 4 feet by 2 feet.
These dimensions are common for most flower shipping carts used by U.S.
speaking, 150 to 200 micromoles of deep red and blue (or white) light from LEDs
is adequate for seedling production based on an average photoperiod of 16
hours. This seed germination cart design would require three or four 4-feet
Production Modules. At 35 watts per module and using an average of $0.10 per
kilowatt-hour, one 4- by 2-feet cart shelf would cost $0.17 per day to light.
The price range for the Production Module depending on the length installed is
approximately $150 to $200 per module.  The useful life
expectancy for a Production Module is approximately 25,000 hours at 90% light intensity and 50,000 hours at 70%.
Real world experience
Holland, a breeder of F1 and open-pollinated annual and perennial
flower seed in Venhuizen, the Netherlands, recently installed a Philips LED
system. The set up consists of more than 7,000 LED lights (15 percent blue and
85 percent red). The LEDs are expected to last 10 times longer than a standard
fluorescent light system. The return on investment for the LED system is
expected to be less than three years.  Willem Koopman, seed
operations manager at Kieft, told FloraCulture
, that the company had been trialing the system for nearly
four years.
“Now we can start
to benefit from this fresh technology,” Koopman said. “This will include a 30
percent cost savings on our energy bills and will increase the efficiency of
our testing services by providing a more consistent light to our young
“We use the
special lighting in our germination testing chambers for our new and upcoming
products before they go on sale so that we can reliably inform the growers of
how many seeds will successfully turn into the premium product which we are
known for. Using this new system will also mean that the seedlings require less
watering because they will not dry out as quickly.”
Dr. Johann Buck
is technical services manager, Hort Americas, Euless, Texas,; David Kuack is a freelance
technical writer in Fort Worth, Texas,

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