The key: cool LEDs

Home Technologist 05 High-tech farming The key: cool LEDs

LEDs are cool enough to fuelling vertical farming.

Vertical farming

“LEDs really hold the key to all this because until they came along five years ago we couldn’t break sunlight down to its component wavelengths,” says Martin McPherson, science director at Stockbridge Technology Centre (STC) near Leeds in the UK, a commercial (and formerly government run) applied research lab that, alongside Philips, is testing vertical farm enabling technologies on a 200 m2 vertical farm. In addition, he says, because LEDs run cool, unlike fluorescent and sodium lamps, it’s that lack of heat rising from the light sources that has put the “vertical” in vertical farms. “LEDs are cool enough to give you the opportunity to stack crops.”

The LEDs fuelling vertical farming are customised variants of the semiconductor light-emitting diodes that many of us are now installing in our homes to replace power-hungry incandescent and fluorescent lamps. But instead of producing white light for the home, tweaking the chemical constituents and layer geometries in the LEDs themselves allows them to be tuned to produce light of just about any wavelength. And what photosynthesis demands at the very least is light at both the blue and red ends of the visible spectrum – blue at a wavelength of 450 nanometers and red at 670 nanometers.

Glasshouses still use inefficient, energy-hogging high-pressure sodium lamps as grow lights – but their yellow-orange light is not well geared for plant growth. “We have found it is much easier to make LEDs produce the right wavelengths for growth,” says Udo van Slooten, a vertical farming expert at Philips LED Horticulture Solutions in Eindhoven, the Netherlands.

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LEDs tailored for specific crops allow 20 to 25 harvests a year at Green Sense Farms, near Chicago, while using 85 percent less energy than traditional systems. “It’s much easier to make LEDs produce the right wavelengths for growth,” says Udo van Slooten of Philips’ LED Horticulture Solutions in the Netherlands.

Alongside their partners at STC and the University of Wageningen in the Netherlands, they are also finding that the placement of the LEDs is crucial, depending on the crop. “A tomato crop can grow very high, so just lighting them from above means leaves at the bottom stay in the shade, so we are placing some LEDs right inside the crop, which we call interlighting,” says van Slooten.

What has surprised the team at STC is the sheer level of control they have over the fate of a crop simply by changing the LED light wavelengths they are bathed in. “You can actually change the architecture of the plants by changing the light spectrum. So you can make ornamental plants and flowers, for instance, remain in a dwarf state without using chemical plant growth regulators. So we can minimise chemical inputs,” says McPherson.

And they can also change vegetable colours: the flavoursome red leaves in a bag of supermarket salad are hard to get in northern Europe during the autumn and winter months so food suppliers have to import the red leaves from southern European sources. “But we can make red-leaved varieties of lettuce express that intense red pigmentation at the flick of a switch, turning on a different set of LEDs.”

“The only problem we have got now is the cost of LED lights. As with any new technology it is expensive at first. For tomato production, for instance, you need an investment of 1 million pounds per hectare for the lighting technology,” says McPherson.

By Paul Marks @PaulMarks12

Related reading: “Growing spinach where the sun doesn’t shine”

Vertical Farming

Journalist: Henry Muller // Graphics and research: ONLAB

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