The basic needs of a crop are clear to any grower who has been through a growing cycle. Why, then, if light is one of the bare necessities of a plant, is it one of the least understood factors of greenhouse growing?
According to Dr. Johann Buck of Hort Americas, LLC, it’s a little more complicated than it seems.
“With numerous units of measurement such as the footcandle, lux, lumen, Watts per square meter, micromoles per square meter per second, moles per day, and associated abbreviations such as PPF, PPFD, and DLI, it’s easy to get confused,” he explains.
In addition, Buck says lighting often isn’t deemed as important as plant nutrition. “Many cut costs by reducing temperature and proper lighting,” he says. “If one of these components is deficient, it can affect the overall growth and quality of the crop.”
Barry Goldsher, president of Growers Supply at FarmTek, agrees. “It’s important to supplement natural light in greenhouses to allow for longer days as well as to overcome obstacles that reduce light transmission,” he says. “Greenhouse glazing, any hanging equipment, and the greenhouse frames themselves can all block light.”
The Ups And The Downs
With supplemental lighting being necessary due to the essence of the greenhouse structure itself, one has to wonder why LED (light-emitting diode) lighting, which is often hailed as the most energy efficient source of illumination, is not being used everywhere.
One reason is the expense of installing LED lighting, says Goldsher.
“The return on investment depends on several factors including the crop/application, production method, interlighting, photoperiodic lighting, cost per kWh of electricity, number of hours of operation, desired light intensity, etc.,” adds Buck.
“In a system-to-system comparison, HID (high intensity discharge) and LED are essentially equal, with HID being a less expensive capital investment,” he continued.
One caveat does apply, however. “The cost of maintenance is less with LEDs,” says Buck. “Within the next three to five years, LEDs designed for horticulture have the potential to replace HID lamps in greenhouse lighting.”
The varying opinions on cost and return could be because “LED manufacturers base their formulas on indoor growing [growers producing in structures such as warehouses] rather than commercial greenhouse growing,” adds Ron James of PARSource Greenhouse Lighting. “Commercial growers are not running lights year round like indoor growers. They are typically running four months out of the year.”
The end result is the return on the investment can take much longer than anticipated, says James. Another drawback he mentions is it is often difficult for growers to see disease symptoms under LED lights.
Benefits Of LED
There is no doubt, though, that LED lighting has its benefits. According to James, the spectral output is much better in LEDs than in other lamps.
Buck adds that the lifetime of the light itself is an often mentioned advantage. “LEDs allow growers to place shelves closer together compared to shelves using fluorescent lighting,” he adds.
Goldsher mentions lower energy bills and that “light intensity is greatest if the light source is closer to the plant. LED lights produce no heat so they can be almost on top of the plants.”
Colored lights are another benefit. Available in different colors, this is a draw for various reasons.
“The [colored lights] are combined depending on the crop,” explains Buck. “For example, blue and red LEDs are often found together since each color is beneficial for photosynthesis.”
Another major benefit is that LED lights can mimic the light of the sun. “Photons are photons, regardless of the lighting source,” concludes Buck. “As long as they are in the right waveband and provide the correct amount of energy to elicit a photosynthetic response, they’ll work.”