Seed Germination Using LED Lights
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 effect at all. Some 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 can be used to provide supplemental light for both germination and growing-on of a crop, especially during dark weather periods and the shorter days of the year.
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 heat.
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.
Generally speaking, 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. growers. Generally 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-foot Production Modules. At 35 watts per module and using an average of $0.10 per kilowatt-hour, one 4- by 2-foot 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. The average grower will use a module for approximately 90 days during the year. Therefore, a module could last 17 years and would only lose 10 percent of its maximum light intensity.
Real World Experience
Kieft-Pro-Seeds Holland, a breeder of F1 and open-pollinated annual and perennial flower seed in Venhuizen, the Netherlands, recently installed a Philips LED system. The setup 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 International 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 seedlings.
“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
Technical Services Manager
Dr. Johann Buck is technical services manager, Hort Americas, LLC, Euless, Texas. Contact him at [email protected]
Freelance Technical Writer
David Kuack is a freelance technical writer in Fort Worth, Texas. Contact him at [email protected]