Optimization of photoperiod and photosynthetic photon flux density (PPFD) for lettuce in plant factories and construction of growth model

• Exploration of static and dynamic light strategies in plant factories. • Dynamic light regulation enhanced lettuce growth and quality. • Dynamic light regulation can effectively optimize and significantly enhance energy use efficiency. Controlled environment agriculture, particularly plant factories, provides a promising approach for addressing challenges caused by extreme climates and declining arable land resources. Light environment regulation is a core technology in plant factories that can directly shape crop growth and quality. In this study, the effects of static photoperiod and dynamic light regulation on lettuce growth, photosynthetic performance, nutritional quality, and energy efficiency were systematically examined, and a growth prediction model was established based on cumulative light integral (CLI). Under static light regimes, a 16 h d -1 significantly enhanced plant height, leaf number, leaf area, stem diameter, chlorophyll content, and photosynthetic parameters compared with 10, 13, and 19 h d -1 treatments. Although a 19 h d -1 photoperiod increased biomass, it inhibited normal morphological development. Under dynamic light regulation, T3—characterized by coordinated, stage-specific adjustments of photoperiod and PPFD—outperformed constant light regimes (200 μmol·m⁻²·s⁻¹/20 h d -1 and 250 μmol·m⁻²·s⁻¹/16 h d -1 ), increasing biomass by 6.89–31.95 %. This advantage was associated with improved photosynthetic adaptation, including more efficient light energy utilization, sustained carbon assimilation, and reduced excitation pressure under varying growth stages. Extended light exposure promoted soluble sugar and ascorbic acid accumulation, whereas dynamic lighting enhanced protein synthesis and reduced nitrate content. Energy analysis indicated that the 16 h d -1 static regime achieved the highest efficiency among fixed treatments, while T3 was the most effective dynamic strategy. These findings demonstrate that dynamic light regulation under equal CLI synergistically improves the photosynthetic productivity, nutritional quality, and energy efficiency. The CLI-driven model can provide robust predictive insights into plant growth, offering a theoretical and technical foundation for precise light management in plant factories.