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Giving crops “micro-naps” saves one-third of indoor farm energy

Flicking LEDs rhythmically on and off could bring down the carbon footprint of indoor farms—while keeping harvests high.
August 2, 2019

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Growing plants under a slow disco of pulsing lights could reduce the energy-use of LED-fueled indoor farming by more than a third, finds a new study. Even better, the research suggests that this method won’t reduce harvests.

Researchers on the new paper made their discovery by tweaking the regular 12-hours-of-light, 12-hours-of-dark cycle under which indoor crops grow. This pattern mimics natural light cycles in the outside world – but the LED lights that create this effect also guzzle large amounts of electricity. For farmers, that creates “a huge cost, about 25% of the operation budget,” says Kevin Folta, professor in the Horticultural Sciences Department at the University of Florida, and author on the new paper. 

So, Folta and his colleagues pondered whether incrementally changing the periods of light and darkness under which they left the plants would save on energy. Testing their idea on seedlings of kale, turnip, beet, and thale cress, they discovered – surprisingly – that exposing these plants to five seconds of light, then plunging them into darkness for ten seconds, cut energy use by 30%, without disrupting the plants’ growth. (It remained the same as it did under the regular 12-hour on-off cycle.)

When the researchers turned it up a notch – increasing the dark pulses for up to 20 seconds (while maintaining the light periods at five-seconds-long) – the seedlings’ productivity was only slightly affected, but it allowed a whopping  60% reduction in electricity.

These optimal light-dark cycles were discovered through a process of trial and error. When the researcher first started out, they subjected the plants to six hours of alternating light and dark, then three hours, then one hour, then 30 minutes. But under all these conditions the plants reacted as if they’d grown only in the dark. The researchers speculate that these slower stretches of light and dark mess with the plants’ internal clocks, which then disrupts their growth.

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Folta thinks that the more rapid five-second-ten-second flickers override the plant’s regular rhythms. “Five second pulses just keep the ‘clock’ starting and stopping to the point where it never really gets going,” Folta told Anthropocene. “The ‘clock’ never really moves and the plant just adjusts to the external environment without paying attention to that internal information.”

These findings matter, because as we seek more innovative ways to produce different types of food, indoor farming will grow in prominence – and we’ll need to find ways to reduce its footprint. Farming crops like herbs, lettuce, strawberries, and tomatoes indoors can bring potentially large environmental savings: producing layers of food in the confines of a warehouse requires less land, fertilizer, and water than crops grown conventionally in the fields. Plus, it brings food closer to the populations it’s intended for – cutting out the massive transport costs of regular farming, and saving on emissions.

Yet, the light energy required to power these farms – plus the energy needed to keep their interiors cool, under all that high-intensity light – risks undoing this good. “We should always be thinking about the carbon footprint of food production,” Folta says. “Not shipping it a far distance is great – but not if it takes a ton more energy to run the lights!” 

Next up, Folta and his colleagues will be experimenting on different types of crops, using different wavelengths and light intensities to determine the ideal low-energy conditions under which plants can grow. They’re also starting to breed plants especially for this artificial indoor environment, to see if they can push the energy-efficiency of indoor farming even further, Folta says. “These are the questions we are wrestling with next.”

Source: Folta et. al. “Manipulation of seedling traits with pulsed light in closed controlled environments.” Environmental and Experimental Botany. 2019. 
Image: AgriLife today via Flickr

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