Could ‘targeted' LEDs be the future of extraterrestrial horticulture? According to researchers at Purdue University, these tiny electrical components could lead a revolution in fine-tuning food production off (and on) Earth.
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Space exploration is a resource-intensive endeavor, especially if you throw humans into the mix. Everything from life support to water supply to waste disposal need to be carefully controlled when supporting astronauts in orbit. The International Space Station, for example, is a grand experiment into how to keep astronauts alive and healthy in a microgravity environment. But the orbiting outpost is only a couple of hundred miles from the Earth's surface, so supplies can be shipped from Earth -- creating a self-supporting biosphere isn't a possibility.
Supporting long-duration spaceflight beyond Earth orbit, however, is an entirely different challenge.
Current plans for manned exploration of Mars would require months of supplies of food and water to be packed on board the transiting spacecraft and if we ever see a human presence on the Red Planet's surface, we'll need to see a paradigm shift in how we supply and produce food in an alien environment. Put simply, for a 1,000 day round-trip to Mars, there is no (practical) way we can pack that quantity of supplies for the voyage.
Cue the space greenhouse, where all your fresh food dreams will become a reality. Although there have been promising experiments into growing produce in space, there are many unknowns and some huge drawbacks that could seriously limit humankind's next giant leap into the solar system.
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If you've seen concept art of greenhouses on Mars or the moon, you'll notice that power-intensive lamps are envisaged to provide light for the various leafy crops. On Earth, sodium lamps are often used to simulate sunlight, but this technology highlights an obstacle for in-space farming.
"Everything on Earth is ultimately driven by sunlight and photosynthesis," said Cary Mitchell, professor of horticulture at Purdue University in a press release. "The question is how we can replicate that in space."
First and foremost, conventional lamps would require huge amounts of power in a place where power is a precious commodity. Not only that, they are inefficient, generating excess heat that may prove hard to manage in a delicately-balanced habitat on Mars and beyond.
In hydroponics research headed by Mitchell and masters student Lucie Poulet (who is now at Blaise Pascal University in France), a silver bullet for the viability of growing produce in space has possibly been found: red and blue light-emitting diodes, or LEDs.
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LEDs have revolutionized miniaturized light generation on Earth. LEDs are highly efficient, lightweight and consume very little power - therefore an obvious choice for a range of in-space applications, now including horticulture.
"If you have to generate your own light with limited energy resources, targeted LED lighting is your best option," said Mitchell. "We're no longer stuck in the era of high-power lighting and large, hot, fragile lamps."
"(Conventional) lighting was taking about 90 percent of the energy demand," added Poulet. "You'd need a nuclear reactor to feed a crew of four people on a regular basis with plants grown under traditional electric lights."
Through experiments on lettuce, Mitchell and Poulet found that high-intensity LEDs were smaller and longer lasting than conventional light sources and they emit negligible radiant heat. In other words, the light-generating components of a space greenhouse can be tiny and positioned extremely close to the photosynthesizing plants without scorching the leaves.
"Instead of the minimum 4-foot (120 centimeters) separation we had between conventional lamps and lettuce, we could get LEDs as close as 4 centimeters (1.6 inches) away from the leaves," said Mitchell.
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Most interestingly, with LEDs, the wavelength of light they emit can be carefully tuned and the researchers have worked out exactly what light the lettuce needs to thrive. Using red and blue LEDs, they found that to optimize photosynthesis, a 95:5 ratio of red and blue LEDs are required. This strategy results in 90 percent less electrical power required over conventional lighting and 50 percent reduction in power required over broad-spectrum LED lighting.
Where space research leads, terrestrial applications often follow. Although the primary focus is on producing lettuce in space, this research could help optimize farming techniques and technologies on Earth.
The next step for this research is to optimize growing conditions still further, regulating how much LED light the lettuce receives depending on its growth cycle. One could envisage "smart" farming where, depending on the crop, the LED light can be boosted or dimmed automatically, optimizing photosynthesis while saving further energy resources.
Source: Purdue University