Determination of LEDs arrangement in a plant factory using a 3D ray-tracing simulation and evaluation on growth of Cucurbitaceae seedlings

When producing seedling scions/rootstocks in a plant factory with artificial lighting (PFAL), uniformity of the lighting environment is an important factor affecting seedling quality in terms of morphological traits, growth, and development. The objectives of this study were to propose an optimal light emitting diodes (LEDs) bar array in a PFAL by 3D ray-tracing simulation and to evaluate the growth of cucumber and watermelon scions/rootstocks using the proposed PFAL light environment. In order to prevent the concentration of light in the center, 7 scenarios were set by adjusting the position of 5 LEDs bars. Light uniformity was verified with 3D ray-tracing simulation. Based on the selected array scenario, LEDs were installed in the module. The simulated and measured light intensity values at the same module locations were compared. Additionally, the growth characteristics of cucumber and watermelon seedlings grown in PFAL were investigated. Among the LEDs array scenarios, scenario seven with the coefficient of variation (CV) value of 18.5% had the highest illuminance value of 267.5 µmol m^{− 2} s^{− 1}. When comparing the simulated and measured light intensities in an empty module without plants, R² = 0.90 and RMSE = 15.09 were obtained, which was consistent at a high level. In this study, we proposed a lighting arrangement for uniform light distribution in PFAL during the production of cucumber and watermelon seedlings, which is expected to help in stable seedling year-round production.