Effects of LED Lighting Configurations on the Growth and Quality of Arugula (Eruca sativa Mill.) in a Vertical NFT System

In vertical farming systems, defining suitable lighting strategies is essential for improving crop productivity and product quality under controlled environmental conditions. This study evaluated the effects of four LED lighting configurations differing in spectral composition and lamp-to-canopy distance on the growth and selected quality traits of arugula (Eruca sativa Mill.) grown in a vertical nutrient film technique (NFT) system. Two light spectra were tested: white LED light and a red–blue LED combination, each applied at two distances from the crop canopy (20 and 40 cm). Two experiments were conducted in 2025 in a climate-controlled cultivation unit, and agronomic and quality-related variables were assessed at harvest, including fresh biomass, leaf development, total polyphenols, antioxidant capacity, chlorophyll index, and nitrate concentration. The LW20 treatment, representing a specific combination of white LED lighting, lamp-to-canopy distance, PPFD, and DLI, was associated with the highest fresh biomass, reaching 42.6 g plant−1 in Experiment 1 and 70.9 g plant−1 in Experiment 2, and with the highest total polyphenol content (38.4 mg GAE 100 g−1 FW). In contrast, the red–blue treatments were associated with lower biomass production, while the RB20 treatment showed the lowest polyphenol concentration (26.2 mg GAE 100 g−1 FW). Among the evaluated quality-related parameters, total polyphenols showed the clearest response to lighting conditions, whereas antioxidant capacity, chlorophyll index, and nitrate concentration were not significantly affected. Under the evaluated conditions, LW20 was the most favorable among the four tested lighting configurations for fresh biomass production and total polyphenol accumulation. However, this response should not be interpreted as evidence of white light superiority alone, because spectral composition, lamp-to-canopy distance, PPFD, and DLI were not independently controlled.