Innovator Spotlight: University of Georgia
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.
|Treatments||PPFD||Average DLI||Energy Consumption|
|Sunlight only||Variable||8.4 µmol/m2/d||N/A|
|Non-adaptive||83 µmol/m2/s||10.5 µmol/m2/d||6.80 kWh/light bar|
|Adaptive||150 µmol/m2/s||10.4 µmol/m2/d||6.80 kWh/light bar|
|Adaptive||250 µmol/m2/s||10.5 µmol/m2/d||12.97 kWh/light bar|
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.”
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.