Greenhouse Lighting: Bright Lights, Big Produce

When it comes to greenhouses, not all light is equal, according to Agriculture and Agri-Food Canada (AAFC) scientist Dr. Xiuming Hao, who is researching how light quality can impact plant growth and nutritional value at the Greenhouse and Processing Crops Research Centre in Harrow.

Greenhouses equipped with supplemental lighting systems allow Canadian producers to grow year round and provide high quality produce. They also help maintain market share and allow Canada to compete successfully in national and international markets. However, Canada has low year-round natural light and lack of available light impedes greenhouse production, especially during the winter months. The solution comes in the form of artificial lighting; however crops develop and grow differently when they are supplied with alternative light sources. And not all artificial light is equal.

“Light quality refers to actual spectrum composition of the light, which largely influences plant growth, fruit yield and quality, and the production of health promoting compounds,” explains Dr. Hao. “Light spectrum compositions have not been explored much for how they improve plant growth and fruit yield and quality.”

This research is largely unexplored because until recently there was no alternative to traditional light sources in greenhouses - high pressure sodium lamps or HPS. HPS lighting emits broad spectrum light which makes it difficult to generate specific spectrum compositions for research. However with the recent development of light emitting diodes, or LEDs, this is now possible.

Plant growth, fruit yield, and fruit quality are not only affected by light quantity but also by light quality (spectrum composition), says Dr. Hao. Spectrum composition can also influence the production of certain compounds in the plant; of specific interest is the production of anti-oxidants. Dr. Hao and his team have been analyzing how different light spectrum compositions impact plant growth, fruit yield, and anti-oxidants in cooperation with Dr. Rong Cao’s team at AAFC’s Guelph Food Research Centre. So far, they have identified the optimal light composition to promote anti-oxidant production in mini-cucumbers.

“We are investigating various vertical light spectrum profiles to identify those which improve both fruit yield and nutritional value of greenhouse vegetables. Our ultimate goal is to develop sustainable year-round production strategies to optimize lighting, fruit yield, fruit attributes, and to support the Canadian greenhouse industry.”

- Dr. Xiuming Hao, Lead Research Scientist, Greenhouse Lighting

Another benefit of LEDs is that they have a low surface temperature. This means they can be placed directly inside a crop canopy without injuring the plants, unlike the traditional HPS lighting which is usually suspended above. With LED use inside the crop canopy there is increased light reaching the plants while ensuring that energy use is as efficient as possible; it is about 30-80% more efficient than HPS lighting.

One of the key goals of AAFC research is to increase the profitability of the agriculture sector by improving nutritional attributes through scientific innovation. This focus helps provide Canadians with a variety of beneficial choices and opens up new marketing opportunities for Canada’s farmers and food processors. This research has been funded by AAFC; the AgriInnovation Programs of Growing Forward 1 and 2 from AAFC; and the Ontario Greenhouse Vegetable Growers.

Source: AAFC