Continuous lighting discovery shines light on new energy-efficient way to grow crops indoors

Plants follow a similar sleep cycle as their human counterparts. Both naturally awake during the day and asleep at night, just like us, growers mimic this cycle through the lighting applications used throughout their greenhouse operations – but it can be costly from an energy standpoint. As such, this conventional circadian rhythm is being challenged in plants grown indoors, thanks to the efforts of Dr. Jason Lanoue and the greenhouse physiology team, including Dr. Xiuming Hao and Celeste Little at Agriculture and Agri-Food Canada's (AAFC) Harrow Research and Development Centre (HRDC).

They discovered that using continuous light on greenhouse-grown tomatoes, cucumbers, and peppers can be more sustainable and cost-effective than using a lighting strategy that follows a more traditional 16 hour day followed by 8 hour night strategy. It's a new process that Dr. Lanoue says "was previously thought to be impossible."

So how does it work?

Lights are applied, using a lower intensity, continuously for 24 hours — as opposed to a higher light intensity for a shorter, 16-18 hour photoperiod. This ensures that the plant's overall lighting needs, referred to as the Daily Light Integral (DLI), are met.

"Continuous lighting is the act of constantly giving light to the plant, via a combination of the sun and supplemental lighting fixtures. In this way, the plant is always under light and always photosynthesizing which can translate into more growth. Dr. Hao and I first came up with the idea because of the increasing electricity demand from the greenhouse industry as they move toward year-round vegetable production. This lessens the strain on the power grid. Furthermore, electricity prices are typically cheaper at night, so by utilizing light at night, the grower is also gaining financially."

- Dr. Jason Lanoue, Post-Doctoral Researcher, Agriculture and Agri-Food Canada

However, since plants typically do not like growing under continuous light, the team developed a unique lighting strategy, called dynamic 24hr lighting, which uses a shift in light spectrum and/or intensity between the day and night periods. This allowed the plants to continue growing, stress-free, as well as they would under a traditional photoperiod.

Employing this strategy would allow the grower to maintain the same yield as plants grown under conventional lighting, but has the added benefit of reducing capital costs and electricity costs — an approach that could lessen the strain on the power grid.

"By lowering the light intensity during the day, growers will need fewer fixtures," says Dr. Lanoue, "which reduces capital costs and uses less electricity during peak demand hours by using our dynamic 24h lighting strategy."

At the HRDC, Dr. Lanoue is part of a larger team which completes greenhouse production and physiology research. Their work includes researching all aspects of greenhouse plant biology from different production strategies to in-depth genetics and biochemical analyses. Dr. Lanoue's research focuses mainly on the impact of different lighting strategies on plant photosynthetic performance and yield. 

Dr. Lanoue's continuous lighting discovery has earned him a spot in Fruit & Vegetable Magazine's Top 4 Under 40 — an achievement he shares with the whole HRDC greenhouse team.

"Discovering that we actually can grow plants under continuous light throughout their production period while maintaining yield and reducing electricity cost by up to 30 percent is a big step towards sustainable greenhouse vegetable production."

The next steps in the research include optimizing the lighting strategies to minimize the cost for growers while maximizing yield. The study will also test continuous light on a greater variety of greenh​ouse crops.

Key Discoveries/Benefits

• Though plants grown indoors follow a traditional circadian rhythm similar to that of the humans that care for them, a new discovery by a team at AAFC's Harrow Research and Development Centre has revealed that it is possible to grow certain crops under a continuous application of light under a lower intensity.
• Current lighting applications used throughout greenhouse operations can be costly for growers — and can place strain on the power grid. Applying a continuous lighting strategy could allow the grower to enjoy the same yield for tomatoes, cucumbers, and peppers, but can reduce electricity and capital costs.
• This discovery is being studied further by the research team to optimize the lighting strategy for potential future industry application, as well as testing continuous lighting on a wider variety of greenhouse crops.

Photo gallery

Related information

• Harrow Research and Development Centre
• Alternating Red and Blue Light-Emitting Diodes Allows for Injury-Free Tomato Production With Continuous Lighting. 2019. Lanoue, J., Zheng, J., Little, C., Thibodeau, A., Grodzinski, B., Hao, X. Frontiers in Plant Science. Doi: 10.3389/fpls.2019.01114.
• Continuous Light Does Not Compromise Growth and Yield in Mini-Cucumber Greenhouse Production with Supplemental LED Light. 2021. Lanoue, J., Zheng, J., Little, C., Grodzinski, B., Hao, X. Plants. Doi: 10.3390/plants10020378.
• Light Spectra and Root Stocks Affect Response of Greenhouse Tomatoes to Long Photoperiod of Supplemental Lighting. 2021. Lanoue, J., Thibodeau, A., Little, C., Zheng, J., Grodzinski, B., Hao, X. Plants. Doi: 10.3390/plants10081674.
• The Power of Far-Red Light at Night: Photomorphogenic, Physiological, and Yield Response in Pepper During Dynamic 24 Hour Lighting. 2022. Lanoue, J., Little, C., Hao, X. Frontiers in Plant Science. Doi: 10.3389/fpls.2022.857616.