Purdue University in West Lafayette, Indiana USA, has continued to study the use of LEDs for crop growth. The latest study to come from the University about using LEDs for crop growth found that employing the right combination of red and blue LEDs provides energy efficient lighting for promoting crop growth in contained environments. This finding may help advance the development of crop growth modules for space exploration.
Cary Mitchell, a professor of horticulture, led the research with then-master’s student Lucie Poulet who found that leaf lettuce flourished under a 95-to-5 ratio of red and blue LEDs close to the plant canopy. They found that the LEDs consumed about 90 percent less electricity per growing area than convention light sources that mimic sunlight. They found that the LED targeted lighting used 50 percent less energy than white LEDs that cover the entire spectrum. They published the study in Life Science and Space Research.
Instead of requiring four feet from conventional hot and fragile red and blue light sources, the LED-based light sources required a minimum of just four centimeters. Mitchell said that the study suggests that the model could be a valuable component of vertical farming systems and controlled-environment agriculture on Earth and in space.
“Everything on Earth is ultimately driven by sunlight and photosynthesis,” he said. “The question is how we can replicate that in space. If you have to generate your own light with limited energy resources, targeted LED lighting is your best option. We’re no longer stuck in the era of high-power lighting and large, hot, fragile lamps.”
Because of full and space and power constraints, long-duration space exploration requires a bioregenerative life-support system, which is self-contained, artificial-ecosystem that mimics Earth’s biosphere. A round-trip to Mars and back to Earth with a crew of six, for example, could take about 1,000 days. It would require more food, water, and oxygen than current space vehicles can carry.
Poulet, who is now a doctoral student at Blaise Pascal University in France said, “If we can design a more energy-efficient system, we can grow vegetables for consumption for longer space travel,” she said. “I can imagine a greenhouse on the moon.”
Conventional, large high-pressure sodium grow lights designed to mimic sunlight consume 600 to 1000 watts. According to the researchers, such conventional lamps can scorch plants that are too close, and they require a filtration system to absorb their excess heat. “Lighting was taking about 90 percent of the energy demand,” Poulet said. “You’d need a nuclear reactor to feed a crew of four people on a regular basis with plants grown under traditional electric lights.”
Because they produce very little heat, LEDs can be positioned at strategic positions that are close to the plant canopy to maximize the amount of light that reaches the leaves. So in addition to optimizing the red and blue light output for the lettuce, they placed the LEDs very close to the lettuce plants so that most of the emitted light went towards the plants.
“Instead of the minimum 4-foot separation we had between conventional lamps and lettuce, we could get LEDs as close as 4 centimeters away from the leaves,” Mitchell said.Their lighting system cut the energy consumption needed for plant growth by “an order of magnitude” compared to traditional lighting, Poulet said. Mitchell pointed out that spectrally targeted LEDs could also help make controlled-environment agriculture on Earth more economically viable by reducing lighting costs.
Their lighting system cut the energy consumption needed for plant growth by “an order of magnitude” compared to traditional lighting, Poulet said. Mitchell pointed out that spectrally targeted LEDs could also help make controlled-environment agriculture on Earth more economically viable by reducing lighting costs.
The next step in the research, according to Mitchell, would be to fine-tune when to increase and decrease lighting intensity according to plant growth stage to optimize growing conditions and save even more energy.