Tailoring LED spectra and cultivation systems enhances lettuce productivity and nutritional quality in vertical indoor farming

Light spectrum and cultivation system are major determinants of crop performance in vertical indoor farming and controlled-environment agriculture. Here, we investigated the interaction effects of three LED spectra and two cultivation systems (aeroponic and ebb-and-flow) on the growth, yield, mineral composition, and quality attributes of Batavia lettuce (Lactuca sativa L. 'Capira') grown under vertical indoor farming conditions. Plants were cultivated under LED1 (70% red, 660 nm + 30% blue, 450 nm), LED2 (full-spectrum PAR, 400-700 nm), and LED3 (65% red, 660 nm + 25% blue, 450 nm + 5% white + 5% far-red, 730 nm) at a standardized light intensity of 200 µmol m⁻² s⁻¹ PPFD using a two-factor experimental design. Significant interaction effects between LED spectrum and cultivation system were observed for plant growth, yield, antioxidant-related compounds, nitrate accumulation, and mineral nutrient composition. Among the evaluated treatments, the LED2 × aeroponic combination resulted in the highest yield (5.02 kg m⁻²), biomass accumulation, and a balanced mineral nutrient profile. In contrast, the LED3 × aeroponic treatment promoted higher total soluble solids and phenolic compound accumulation, whereas the LED1 × Ebb and Flow combination enhanced flavonoid content. The highest vitamin C content and the lowest nitrate accumulation were both observed under the LED1 × aeroponic treatment under the evaluated cultivation conditions. Estimated energy analysis further demonstrated that although LED2 treatments required greater electrical energy input, their higher biomass production resulted in energy-use efficiency values comparable to those obtained under LED3 treatments. These results indicate that coordinated optimization of LED lighting and cultivation system design can improve productivity and quality in multilayer vertical farming systems. However, trade-offs among yield, nitrate accumulation, quality attributes, and estimated energy demand should also be considered. Future research should integrate physiological measurements, direct electrical monitoring, and economic analyses to enable more mechanistic and application-oriented optimization of vertical farming systems.