What Research is Finding About Extended Photoperiods in Greenhouse Eggplant

Researchers from Agriculture & Agri-Food Canada (Harrow Research and Development Centre) are learning more about how extending LED lighting hours affects greenhouse eggplant yield and efficiency.

Researchers tested three lighting strategies that delivered the same total daily light but spread it over 16, 20, or 24 hours (using lower intensity for longer periods). The key takeaway: More hours of light did not increase total yield beyond standard 16-hour lighting, but all supplemental lighting dramatically improved production. Yields were 124% to 144% higher than plants grown without added light.

The findings suggest the way light is delivered can be just as important as the total amount applied. Extending photoperiods (e.g., 20 to 24 hours) at lower intensity produced similar yields while offering potential energy cost savings, especially if electricity is cheaper at night. A 24-hour “continuous light” strategy using blue light overnight performed comparably to shorter photoperiods without reducing yield.

There are trade-offs: The 20-hour treatment triggered early plant stress and slightly reduced late-season performance, even though total yield was unchanged. Meanwhile, 16-hour lighting produced the most consistent plant growth.

Editor’s note: This article was originally published in CEAg World’s 2026 Industry Report: Greenhouse Produce.