Targeted LEDs: Photosynthesis Power in Space?

If we end up in space, seeking carrots, bok choy, and other sustaining vegetables, we'll be very glad we have LEDs to power the plants in all that darkness. Or, that's one possibility. In the mean time, it's excellent to expand the ways we can keep plants alive in limited conditions, such as underground, in vertical situations, or in space.

That is, researchers with Purdue University, in a study funded by NASA, have been thinking along those lines, according to a release. They have found that red and blue LEDs used in a targeted way can provide energy-efficient lighting to stimulate photosynthesis. Knowing this could advance the development of crop-growth areas for space exploration.

Cary Mitchell, professor of horticulture, and Lucie Poulet, then a master's student, determined that leaf lettuce grew well under a 95-to-5 ratio of red and blue light-emitting diodes (LEDs) placed near the plant canopy, the release said. Their research was published recently in the journal Life Sciences in Space Research.

The targeted LED lighting also used about 90 percent less electrical power per growing area than standard lighting and 50 percent less energy than full-coverage LED lighting, according to Eurekalert.

"Everything on Earth is ultimately driven by sunlight and photosynthesis," Mitchell said, according to a release. "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."

Ultimately, the goal is to find a way for space explorers on long journeys to have a self-contained ecosystem that mimics Earth's biosphere, the release said. Flying to Mars and back for a crew of six, for instance, could take about 1,000 days. It would require substantial food, water and oxygen--more than current space vehicles can schlep along.

"If we can design a more energy-efficient system, we can grow vegetables for consumption for longer space travel," said Poulet, now a doctoral student at Blaise Pascal University in France, in the release. "I can imagine a greenhouse on the moon."

Slowing that possibility has been the huge energy cost of traditional high-pressure sodium lamps used to mimic sunlight in contained environments.

The researchers turned to high-intensity LEDs, which require about a watt each and are both smaller and longer lasting than traditional lights. They can also be placed right next to the plant canopy, because they emit no radiant heat, the release said.

The red and blue ratio came about because it provides the lettuce with the best combination of lightwaves for photosynthesis and growth, the release said.

Next in the research is, they think, deciding when to increase and decrease lighting to optimize growing conditions and save energy at each growth stage.