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Innovator Spotlight: University of Georgia

Georgia, USA

We selected Fluence to get precise dimming control and uniform lighting at a close distance.Dr. Marc van Iersel, Ph.D., Dept. of Horticulture, University of Georgia

Dimming the Lights for a Brighter Future

University of Georgia refines emerging cultivation methods with controlled dimming and Fluence LEDs.

The more scientists discover about photobiology, the more effectively cultivators can control their crop cycle time, plant quality, energy use, and operating costs. To have dynamic control over lighting conditions in a greenhouse means providing crops with optimal light levels to produce consistent, high-quality crops—all while reducing wasted photons and electricity.

At the University of Georgia’s Horticultural Physiology Lab, researchers are exploring how crop predictability and energy efficiency are affected by providing greenhouse plants with dynamic supplemental lighting. Typically, supplemental greenhouse lighting allows for year-round production by providing a fixed amount of light to increase the daily light integral (DLI) and extend the photoperiod in winter months. Dynamic or “adaptive” lighting control increases supplemental light intensities when ambient levels are low, and reduce the supplemental intensity when ambient levels rise. This increases plant growth by maintaining optimal light levels, and it saves energy by eliminating supplementation in excess of what the plants could use.

“We’re adjusting the light output from the LEDs based on how much sunlight is present, so the LEDs automatically dim when more sunlight is available,” says Dr. Marc van Iersel, lead researcher and crop physiology specialist. “Automated dimming control ensures plants get a consistent amount of light from day to day and LED lights are energy efficient.”

We’re seeing if we can get the same amount of growth with adaptive lighting as you can get with conventional lighting—except with a lower energy cost.DR. MARC VAN IERSEL

All Fluence LED solutions are 0-10V dimmable to deliver exact light intensities from 0-100%. Van Iersel and his graduate students utilize this functionality —in conjunction with a lighting controller developed by Van Iersel’s lab—to make responsive light intensity changes on a second-by-second basis.

His team’s goal was to speed up the rooting process of unrooted rose cuttings and shorten their production cycle. The trial evaluated two adaptive light treatments, one non-adaptive light treatment, and one non-supplemental light treatment which served as a control.

Trial Treatments

For the two adaptive treatments, the photosynthetic photon flux density (PPFD) levels were maintained such that they never dropped below 150 or 250 µmol/m2/s during the 14-hour photoperiod. Therefore, the lights would dim automatically as the amount of sunlight exceeded the target PPFD value, assuring the LEDs never provided more light than could be used effectively by the crop. The non-adaptive treatment received a constant 83 µmol/m2/s for 14 hours per day—regardless of the ambient light level.

Table 1
TreatmentsPPFDAverage DLIEnergy Consumption
Sunlight onlyVariable8.4 µmol/m2/dN/A
Non-adaptive83 µmol/m2/s 10.5 µmol/m2/d6.80 kWh/light bar
Adaptive150 µmol/m2/s 10.4 µmol/m2/d6.80 kWh/light bar
Adaptive250 µmol/m2/s 10.5 µmol/m2/d12.97 kWh/light bar

The Results

Under the first adaptive supplemental light treatment (maintaining a minimum of 150 µmol/m2/s), his team saw increased root and shoot weight over the treatment maintained at a constant supplemental 83 µmol/m2/s from the LEDs (see Figure 1). Notably, the overall electrical input for both of these groups was comparable, yet growth was measurably more robust when controlled dimming was used rather than constant light.

The second adaptive supplemental treatment (maintaining a minimum PPFD of 250 µmol/m2/s), resulted in the highest root and shoot biomass growth—as well as the greatest energy expenditure. These plants rooted one week faster than the control (the cuttings that did not receive any supplemental light). For many crops, the faster bench turns can offset the additional energy cost.

“Ultimately, economists and commercial growers will look at the tradeoff—how much additional money we’ll spend on electricity to shorten the crop cycle,” van Iersel says. “The increased biomass per kilowatt hour of electricity is what we’re looking at now.”

I see LEDs as the future of lighting. Our partnership with Fluence is one we will continue as we expand the research on LED technology and provide insight to improve commercial horticulture operations.DR. MARC VAN IERSEL

Van Iersel notes that his team’s research techniques would not be possible with high-pressure sodium lights—only with LEDs. HPS lights are more difficult to accurately dim; and, because of their heat output, HPS lights cannot be mounted close to the crop. Due to minimal heat output and passive thermal management, the Fluence LED solutions can be positioned close to the canopy, and light intensity can be precisely controlled. Additionally, Dr. van Iersel finds value in the uniform coverage made possible by the Fluence lights’ optic design and form factor.

Dr. Van Iersel intends to design additional experiments with Fluence LED grow lights and to continue partnering with the Fluence Bioengineering team on upcoming spectrum-related research.