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cucumbers growing in an energy-efficient greenhouse

LEDs and greenhouses: researchers are discovering new benefits

LEDs are a more energy-efficient choice for greenhouses than high-pressure sodium lights. Researchers are also looking at how they may improve the quality of fruits, vegetables, flowers and cannabis.

Lighting is one of the biggest expenses for greenhouse operators. In Ontario, and in even warmer, sunnier climates south of the border, greenhouse operators benefit from using supplemental lighting.

Traditionally, greenhouse operators have turned to high-pressure sodium (HPS) lighting, but LEDs are slowly gaining traction. Why? They’re significantly more energy-efficient, offering major potential for cutting overall energy use and operational costs. 

LED grow lights can use between 35 and 55 per cent less energy than HPS lights, according to the Greenhouse Energy Profile Study1 published by the Independent Electricity System Operator in September 2019. Performance standards for horticultural LEDs are also improving, so growers can be even more confident these lights will work well for them.

Along with being more energy efficient and having a longer lifespan than traditional alternatives, LEDs can offer growers more control, so they can experiment with how light influences the quality of their crops. This is because LEDs can be dimmable and start up and power down more quickly than HPS lights. They also offer more focused light and can provide different light spectra (or colour) combinations.

Every plant is different, so depending on what a greenhouse is growing – fruits, vegetables, flowers or cannabis – the benefits of LEDs can come to life in different ways. “Growers need to determine what they want to achieve with lighting – is it improved quality, shorter production cycles, or control of plant habits?” says James Dyck, a researcher with the Ontario Ministry of Agriculture, Food and Rural Affairs.

Researchers across North America are testing and learning about LEDs. Here are just a few positive findings to consider as you decide how to use LEDs in your own greenhouse.

LEDs may get you fuller flowers

Researchers from the University of Guelph conducted an experiment to determine the impact of spectral light on certain ornamental flowers, including marigolds and geraniums.2 They found that pure blue light was more effective at promoting flowering than red light. It turns out that the flower species tested had a “memory” for the blue light in its early growth stages.  

“LEDs can impact the flowering of plants, the growth (height and width), the taste of the fruits or plants, and the nutritional or medicinal content,” says Mike Dixon, an environmental systems researcher and professor at the University of Guelph. “Different light spectra and environment control recipes can manipulate each of these plant responses.”

The researchers also found that the blue light promoted growing in plant stems, which indicates that plants have insufficient light and need to “reach” for it. They suggest growers try using blue light in early growing periods before switching to red light.

For fruits and veggies, the right light recipe matters

Researchers from Canada’s Department of Agriculture and Agri-Food experimented to know more about the impact of LEDs on tomatoes and peppers.3

The researchers performed a continuous lighting experiment on tomatoes, alternating between red and blue light over a 24-hour period. They found this improved fruit yield in the early production period. It also increased plant height and leaf area. In peppers, they found using a hybrid strategy (40 per cent HPS and 60 per cent purple LED) with white LED achieved higher fruit yields in both winter and summer.

LED lights may also improve yields for certain leafy plants. One research study found using 50 per cent blue light for an hour at the end of the day increased lettuce fresh weights (the weight at harvest) by 18 per cent.4 A red-blue light combination boosted fresh weight by just over 11 per cent.5 Cannabis growers may be able to use the same techniques to increase cannabis leaf expansion.

Spectral light may also be able to enhance secondary metabolites, some of which have anti-microbial properties. This means LEDs may help improve the medicinal qualities of plants and deter certain pests. One U.S. study, for example, found that LEDs could boost anthocyanins – which have antioxidant effects – in baby lettuce.3

For cannabis, more light can mean more yield – and more revenue

LED lighting company Lumigrow suggests there is a “one per cent rule” in cannabis production: when lighting intensity increases one per cent, flower weight gain – or yield – increases by the same amount.5

Growers may also be able to use the light spectrum to produce higher-quality cannabis plants, according to Lumigrow. Consistent with this, some research suggests increasing blue light between 13 to 20 per cent decreases height by 10 per cent, allowing growers to produce cannabis with strong root formation, compact form and thicker leaves.5

Along with potentially improving cannabis plant yield and quality, Lumigrow also suggests LEDs may also increase total active cannabinoids per acre (compared to HPS lighting). More active cannabinoids – which include the medicinal ingredients in cannabis – in turn may boost revenue for growers. 

Whatever you’re growing, LEDs are worth a closer look. For greenhouse operators interested in upgrading to these energy-efficient lights, see how Save on Energy incentives can help.

References

1Independent Electricity System Operator and Posterity Group, Greenhouse Energy Profile Study, September 27, 2019.
2Yun Kong, Katherine Vinson, Rebecca Johnson, Devdutt Kamath, Youbin Zheng, Does “Blue” Light Invariably Cause Plant Compactness?, presented at the Greenhouse Canada Conference 2018. 
3Xiuming Hao, Latest Development in Lighting Greenhouse Vegetables, presented at the Greenhouse Canada Conference 2019.
4Youbin Zheng, Are LEDs the right choice for my operation?, GreenhouseCanada.com, March 1, 2016.
5Melanie Yelton, Lighting in Greenhouse Cannabis Production, presented at the Greenhouse Canada Conference 2019.

Note to reader: all references to Greenhouse Canada Conference 2019 presentations can be accessed by visiting the Canadian Greenhouse Conference web page and clicking 2019 Archive Presentations.