Dynamic lighting strategies for crop growth and electricity use in lettuce plant factories: an integrated growth–energy balance modelling study

Lighting schedules in plant factories affect lettuce ( Lactuca sativa L.) growth and the heat and moisture loads managed by environmental control. Five prescribed 25-day lighting schedules were compared using a coupled crop–facility model at equal cumulative incident photon supply (288 mol m −2 ): Cases A (constant), B (staged-increasing), C (guided by reference leaf area index), D (dry-matter-priority) and E (coupled-model-selected). Each schedule was evaluated for 12 cultivation-start months under one typical-meteorological-year weather dataset for Daejeon. In every month, Cases B–E produced greater final modelled whole-plant dry matter than Case A (mean differences, 9.66–11.80 g DM m −2 ). Their mean incident-photon light-use efficiency, calculated from cultivation-period dry-matter gain, was 3.45–4.22 % higher. In some months, mainly October–December, each time-varying schedule also used less LED plus heat-pump electricity than Case A. With identical LED electricity, these differences arose from heat-pump operation. Case E was selected by mean final whole-plant dry matter for January, July and October starts and applied unchanged to all 12 starts. A fixed calendar-based assignment (Case E for December–May, Case D for June–November starts) achieved 99.8 % of the summed electricity-only operating-margin improvement from Case A to the retrospective month-specific maximum using the whole-plant fresh-mass conversion, monthly crop prices and flat electricity-rate proxy. Schedule rankings depended on photon timing, cultivation-start month and valuation criterion. These results are deterministic model predictions for the simulated facility and weather scenario rather than experimental measurements from a physical plant factory. The model can inform lighting-schedule choices by cultivation-start month based on crop growth and electricity.