Continuous lighting for improved microgreen production

The Harrow Research and Development Centre, located in Harrow, Ontario, Canada, is a part of Agriculture & Agri-Food Canada’s network of research facilities. It is the largest greenhouse research facility in North America. Recently, Dr. Xiuming Hao and Dr. Jason Lanoue have turned their interest towards the vertical farming sector. While vertical farming can have a very high yield per unit area thanks to their multi-layer growing platforms, they are resource intensive. The electricity used by the LED lighting system can represent upwards of 20% of operating costs which is second only to labor. What’s more, heat generated by the lighting system and growth facility must be controlled using heating, ventilation, and air conditioning (HVAC) system, which also requires electricity. With energy prices rising throughout the world, it is imperative to find a sustainable solution to reduce energy consumption while maintaining the production of fresh produce.

This paper looks at the impact of continuous lighting on the production of four microgreens: amaranth cv. ‘Garnet Red,’ collard greens cv. ‘Vates,’ green basil cv. ‘Genovese,’ and purple basil cv. ‘Red Rubin.’ Continuous lighting (CL) is the act of giving a plant constant light throughout a 24h period. In this way, a lower light intensity is needed to reach the same daily light integral (DLI). This reduces the light fixture need and thus capital cost making vertical farms a more affordable production option. The use of continuous lighting can also take advantage of reduced electricity prices during the low-demand night period, which is a practice used by many countries and municipalities around the world.           

In amaranth and green basil, the use of CL at the same DLI showed improved fresh biomass production compared to growth under a 16h photoperiod. When the photosynthetic photon flux density (PPFD) remained the same, CL resulted in an increase in yield between 21.1-92.7% depending on species. In all microgreens tested, the electricity-use efficiency of the lights (fresh biomass produced per MJ of energy consumed) was increased when plants were grown under CL, indicating greater biomass conversion efficiency under CL. This improved growth also resulted in a reduced electricity cost per fresh weight produced, which indicates a reduction in operating costs for producers.

Microgreens are prized for their nutrient profile and high antioxidant content making them a functional food. Growth under CL increased total phenolic and anthocyanin content as well as antioxidant activities in amaranth and collard greens. This shows that CL can have a hormetic effect on the nutrient profile of some microgreens species.

To read the complete study, go to

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