Interactive Effects of Spectrum and Intensity of RBW, FR and UV-A on Growth, Photosynthetic Performance, and Antioxidant Properties of Basil and Parsley Grown in Indoor Vertical Farm

Controlling the spectrum and intensity of artificial light offers an effective strategy to optimize crop productivity and nutritional quality in controlled-environment agriculture. This study evaluated the combined effects of red–blue–white light (RBW), supplemented with far-red (RBW + FR), and RBW supplemented with both FR and UV-A (RBW + FR+UVA) at three photosynthetic photon flux densities (PPFDs; 100, 50, and 25 µmol m⁻² s⁻¹) on growth, photosynthetic traits, pigment composition, and antioxidant capacity of basil ( Ocimum basilicum L.) and parsley ( Petroselinum crispum L). Across all light intensities, RBW + FR consistently enhanced vegetative growth in basil, increasing growth and biomass accumulation compared with RBW alone. In contrast, RBW + FR+UVA generally reduced growth but increased anthocyanin concentration, phenolic and flavonoid contents. Basil exhibited higher chlorophyll content, photosynthetic performance index (PI), and stomatal conductance under RBW + FR, particularly at 25 µmol m⁻² s⁻¹, indicating improved photosynthetic efficiency under low-light conditions. Parsley showed a weaker growth response to spectral treatments but demonstrated substantial increases in total phenolic content, flavonoids, and DPPH free-radical scavenging activity under RBW + FR+UVA, especially at reduced PPFDs. Overall, FR radiation primarily stimulated growth and photosynthetic performance, whereas UV-A acted as a biochemical elicitor, enhancing antioxidant capacity at the expense of biomass. These species-specific responses highlight the importance of tailored spectral strategies to balance yield and nutritional quality in low-energy indoor farming systems.