Supplemental lighting shines down on greenhouse tomatoes.
© Gert Van Santen |

Between various new LED and HPS lights and fixtures, produce growers face a wide range of lighting options. In these pages, researchers and manufacturers look at what’s new and in store for growers.

Individual growers have their own goals they need to consider to make the right lighting decision, says Paul Gray, vice president of horticulture lighting solutions at illumitex. “You can be growing basil in a greenhouse in, say, Leamington, or in the Niagara Falls area — and it may be different just in terms of how one operation works versus another,” he says. “That obviously will then dictate what we do in terms of a lighting offering and how economic we can make it, based upon what that grower or what that operation’s main primary goals are in terms of their quality, their yield and things of that nature.”

People are often set in their ways, Gray says, but he sees a future in light-emitting diodes (LEDs). Growers can fully adopt LEDs or trial them. In the case of a trial, he says, "make sure that it’s representative — in other words, that you can get the facts and you get enough confidence that if you’re going to go, then, beyond the trial, that you’re making the right decision,” he says.

Other markets, such as homes, automobiles, appliances and traffic lights have adopted LED lights, Gray says. Right now, LED use in horticulture encompasses only a single-digit percentage of total LED use, but he expects a full LED takeover in horticulture. And, he says, the economics are ripe for this to occur.

When Ricardo Hernandez, assistant professor in North Carolina State University’s Department of Horticultural Sciences, began conducting lighting research several years ago, he predicted the future of horticultural lighting would be in LEDs. More work still has to be done with LEDs, he says, but there is “no question” that they represent the future of lighting because of the increasing amount of efficiencies in lights and fixtures. “The lowest-hanging fruit, or the quickest evaluation, will be in supplemental lighting, and then you’re going to have all the other options, such as vertical farming and unique recipes for unique crops,” he says.

Lighting researchers are deploying diverse research and strategies, but working together in a synergistic way, Hernandez says. He and some others are focused on photomorphogenesis, while others are more focused on fixture efficiencies and plant responses to light intensity.

Some of the newest developments in lighting for indoor produce operations relate to efficiency, light intensity management and the independent control of wavelengths, Hernandez notes. Much of the research that he and other researchers are currently conducting will likely manifest into technologies that will become more accessible to growers in the future.

Hernandez offers a comparison to computers to illustrate how growers will eventually be able to easily use LEDs. “A computer is a very complicated machine, but for us, it is very easy to use now,” he says. “So, in the future, having an LED fixture with the ability to change intensity, colors and photoperiod by being programmed to a specific crop, should be something easy for the grower.”

Some of the biggest hurdles for growers when it comes to maximizing lighting use is the cost of the technology — which Hernandez says will decrease over time — as well as acquiring knowledge regarding the technology, such as which lighting or fixtures to use. “My advice is just to listen to the manufacturers and also do a little bit of research yourself — university-based research — and that will probably give you the best answer to your needs,” he says.

LEDs often come to mind in the context of lighting developments in indoor agriculture.
Photo: Karen E. Varga

Both Hernandez and PARsource division manager Ron James make the point that lighting for horticulture is more nuanced than lighting for human use. For instance, James says, the light spacing for growing plants needs to be closer together than the light spacing for architectural applications.

PARsource bases its lighting designs on numerous factors. “When we do our designs and we’re moving around and we’re calculating the overlap, there’s times that this reflector’s better, there’s times that this reflector’s better and there’s times that this reflector’s better,” James says. Reflector designs are based on light spectrum, but also on factors such as light distribution and uniformity.

James recommends growers work with a lighting manufacturer that sells all technologies so that they can find the right fit. Growing conditions vary for growers in different locations, operating under different conditions and growing different crops. For example, greenhouse produce growers in Michigan versus Texas, or growing tomatoes versus lettuce, need different amounts of light.

With LEDs, James says, growers can control the spectrum and don’t have to worry about there being as much heat as with other light types. Other newer lighting technologies include double-ended high-intensity discharge (HID) lights and ceramic metal halide HIDs, James says. Double-ended lamps have a high PAR output and more blue light than high-pressure sodium (HPS) lamps. Ceramic metal halides also give off a large amount of blue spectrum light, and they have a double-glass jacket. “Metal halide is more for vegetative growth versus fruiting flowering, and that’s why people kind of like it,” James says.

Many companies want to replace 1,000-watt HPS lights with LEDs, but Dr. Thomas Schwend, photobiology specialist at BLV Licht- und Vakuumtechnik, says LED lights are not yet customized enough to fit growers’ various needs. “We focus on even better HPS lighting,” he says. “Better HPS means high quality lamps with a higher light output (like the 2100 µmol –s lamp we introduced some time ago) that shows an extreme stability over the entire life time.”

For growers to work in a controlled environment by definition means their crop is placed in the perfect climate, Schwend says. In addition to light efficiency, growers have to manage consistent temperature, carbon dioxide, humidity, irrigation and fertilization. “If you want to maximize your yield you have to take all parameters into consideration,” he says. “For instance, there is a strong interaction of light and temperature. We can only advise growers to use a climate computer. It can save energy and increase efficiency in many ways. For instance, by using a daily light integral function.”

Climate is important for optimizing crop yields, saving energy and managing pests, Schwend says. In controlling climate, lighting plays a significant role.

For the lighting industry to move forward, lighting companies, researchers and growers need to work collaboratively toward a common goal of improving horticultural lighting. “Progress in the field can be achieved only by working close to the grower,” Schwend says.