LEDs in greenhouses deliver same yield as grow lights, using just 25% of the energy

LED grow lights
© Purdue Agricultural Communication

Even with our growing emphasis on and awareness of the benefits to the environment when eating locally and seasonally, there hasn't seemed to have been a major shift in our eating habits, as most of us still want to be able to buy any kind of produce we want, any time of the year that we want, regardless of the conditions necessary to grow those items.

We expect to find things like ripe, flavorful tomatoes and peppers in the grocery store during the middle of winter, and we also expect them to still be affordable. That's a tall order, especially in the northern parts of the world, as maintaining heated, lighted greenhouses all winter long consumes quite a bit of energy and money, which is something that small and local growers in the north can't generally afford to do.

To be able to still meet demand in the winter for out-of-season items such as tomatoes, grocery stores and restaurants depend on produce trucked in from a thousand miles away, with is also responsible for large amounts of energy consumption for transport and refrigeration. Those heavily-traveled tomatoes are often bland in flavor and high in cost, but still end up cheaper to produce than growing them locally.

"The average tomato is trucked 1,500 miles from where it’s picked in the winter and it sits on that truck for a week or more. By the time it gets to a northern market, it has been in the dark for a while and its quality is degraded. Yet you pay a premium for it—up to four dollars a pound in January." - Cary Mitchell, Purdue University horticulture professor

However, LED lights may soon enable greenhouse growers to grow affordable, vine-ripened tomatoes and other produce items much closer to the market, enabling more local food production, especially in the northern latitudes.

The results of a Purdue University study show that by using LED lights instead of the conventional high pressure sodium (HPS) lights for growing tomatoes in greenhouses, growers could get the same yields of fruit from the plants using just 25% of the energy required with current methods.

Because the LEDs produce far less heat than HPS lights, they can be placed very close to the plants to deliver high intensity lights to the surface of the leaves, including the lower branches and leaves in the understory.

"The leaves are photosynthesizing on the lower parts of the plants, and that may be helping with the plant's energy. We're getting the high intensity of the LEDs close to the plants because they're not hot like a high-pressure sodium lamp. If you put one of those close to the plants, you'd scorch it." - Celina Gómez, doctoral student

According to Txchnologist, only 30% of the energy going into an HPS light gets converted to usable light, with the other 70% being lost as heat, whereas LEDs can convert up to 50%, and can be optimized for different wavelengths that favor plant growth.

The study, which is published at HortTechnology, found that each plant grown using traditional HPS lighting used 1224 kilowatt-hours of energy through the season, while those under LEDs consumed just 294 kilowatt-hours.

That's a significant savings in energy, and therefore money, which could be just the advantage needed for local growers to compete with trucked-in produce during the winter seasons.

"The United States still imports one-third of its tomatoes from Mexico and Canada, as well as other countries. This technology could allow U.S. growers to create local jobs that shrink carbon footprints and produce better-tasting tomatoes." - Mitchell

LEDs in greenhouses deliver same yield as grow lights, using just 25% of the energy
Using LED lighting instead of traditional high pressure sodium lights to grow tomatoes in greenhouses during the winter could cut costs and boost local food production.

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