Optimizing growth efficiency and energy economics in vertical farming through dynamic reduction of blue light in lettuce baby leaf (Lactuca sativa L.)

Introduction: Vertical farming offers a sustainable solution for urban food production, but energy optimization remains a critical challenge, with nearly half of the electricity requirements dedicated to artificial lighting. Dynamic adjustment of blue and red light can reduce energy costs, as blue light is more energy-intensive, thereby lowering operating expenses and increasing profitability.Methods: This research investigates the effects of dynamic adjustment of blue and red light on lettuce (Lactuca sativa, cv. Danstar) plants. Four light treatments were tested, each maintaining a total photosynthetic photon flux density (PPFD) of 200 μmol m-2 s-1 under a 16-hour photoperiod: (1) RB3 (control, 150 μmol m-2 s-1 red and 50 μmol m-2 s-1 blue); (2) 25% blue (B) reduction with hourly alternation between control and 175 μmol m-2 s-1 red/25 μmol m-2 s-1 blue; (3) 38% B reduction with hourly cycling through RB3, 162/38, 175/25, and 188/12 μmol m-2 s-1 of red/blue light; and (4) 50% B reduction with hourly alternation between control and 200 μmol m-2 s-1 monochromatic red. Agronomical, physiological, and morphological data were collected weekly from 7, 14, and 21 days after transplanting.Results: While the 50% B dynamic treatment did not enhance overall crop performance compared to the RB3 control, 25% B and 38% B increased lettuce fresh yield by 50-60%, with dry weight remaining stable.Discussion: These responses indicate improved leaf hydration (reduced dry matter content) resulting in increased fresh marketable yield, improved light-energy use efficiency by up to 63% and reduced lighting costs by 40%, demonstrating that constant blue light at a fixed PPFD is not required for optimal growth. This approach may offer a viable strategy to reduce production costs and enhance sustainability in controlled environment agriculture.