Red:Blue LED Ratio Modulates Growth and Nutritional Quality of Brassica Microgreens Under Low Daily Light Integral

Growing consumer interest in nutrient-dense greens has increased demand for microgreens, which are widely produced indoors under LED lighting. Light quality, especially red and blue lighting, strongly influences microgreens’ growth and nutritional quality, and optimizing their combination is critical. This study evaluated how different red:blue LED ratios affect yield and nutritional composition of radish and broccoli microgreens grown under a 14 h photoperiod and six LED treatments (100% white, red, or blue; and red:blue ratios of 50:50, 25:75, and 75:25) at 163 μmol m−2 s−1 PPFD, on average. Radish and broccoli were harvested 7 and 8 days after sowing, respectively. Microgreens grown under 100% blue, red, or white LED were taller than those under mixed red:blue treatments, with 100% blue producing the greatest shoot elongation but the lowest dry biomass. Antioxidant activity was highest under 100% blue radiation (16.3% increase across species) and lowest under 100% red. Mineral composition also varied with light quality. The 75:25 red:blue treatment produced the highest nitrogen content (6.42 g 100 g−1 vs. 5.89 g 100 g−1 under red). In broccoli microgreens, the 25:75 and 75:25 red:blue treatments resulted in the highest iron concentrations, 15–20% higher than monochromatic red, blue, or white treatments. Overall, these results support previous evidence that blue radiation enhances secondary metabolite accumulation, while mixed red and blue light influences mineral uptake. These findings highlight the importance of LED spectral optimization to maximize microgreen commercial and nutritional quality in controlled-environment production systems.