Considerations of utilizing far-red light in the production of leafy-green vegetables indoors

Utilizing far-red (FR; 700-750 nm) light can increase the energy-use efficacy and economic viability of indoor vertical farms because it increases photosynthesis and promotes extension growth, which leads to greater photon capture and biomass accumulation. In addition, discrete FR light-emitting diodes offs often exist with FR light including undesirable decreases in phytochemical concentrations, foliage coloration, and shelf life. Therefore, a comprehensive understanding of the potential advantages and disadvantages of FR light is important when utilizing FR light in indoor leafy-green vegetable production. A meta-analysis of scientific publications indicates that FR light increases leaf length to a greater degree than leaf area per plant. The analysis also showed that FR light promotes biomass accumulation but to a lesser extent than morphological alterations. This review discusses FR light descriptions and estimators and summarizes research-based information on its effects on leafy-green species grown under solesource lighting including plant morphology, growth and biomass accumulation, phytochemical concentration, foliage pigmentation, and shelf and storage life. In addition, differences between FR light substitution and supplementation are discussed from both research and practical perspectives.