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The widespread application of LED plant factories has been hindered by the high energy consumption and low light use efficiency. Adjustment of the daily light integral (DLI) offers a promising approach to enhance the light use efficiency in hydroponic cultivation within LED plant factories. However, most LED plant factories use a constant DLI during the cultivation process, which often leads to excessive light intensity in the early growth stage and insufficient light intensity in the later stage. To address this issue, this study aimed to improve the photon yield of hydroponic lettuce by optimizing the DLI at different growth stages. A logistic growth model was employed to segment the lettuce growth process, with variable DLI levels applied to each stage. DLIs of 11.5, 14.4, and 18.0 mol m−2·d−1 were implemented at the slow growth stage, and the DLIs were adjusted to 14.4, 17.3, and 21.2 mol m−2·d−1 at the rapid growth stage. Photoperiods of 16 h·d−1 and 20 h·d−1 were used for the two growth stages, and LED lamps with white and red chips (ratio of red to blue light was 1.5) were used as the light source. The results indicated that the photoperiod had no significant impact on the shoot fresh weight and photon yield under the constant DLI conditions at the slow growth stage (12 days after transplanting). The 14.4 mol m−2·d−1 treatment resulted in the highest photon yield due to the significant increases in the light absorption and net photosynthetic rate of the leaves compared to the 11.5 mol m−2·d−1 treatment. No significant differences in the specific leaf area (SLA) and leaf light absorption were observed between the 14.4 and 18.0 mol m−2·d−1 treatments; however, the photon yield and actual photochemical efficiency (ΦPSII) significantly decreased. Compared with the DLI of 14.4 mol m−2·d−1 at the rapid growth stage (24 days after transplanting), the 17.3 mol m−2·d−1 treatment with 20 h·d−1 increased the leaf light absorption by 5%, the net photosynthetic rate by 35%, the shoot fresh weight by 25%, and the photon yield by 19%. However, the treatments with DLIs above 17.3 mol m−2·d−1 resulted in notable decreases in the photon yield, ΦPSII, and photosynthetic potential. In conclusion, it is recommended to implement a 20 h·d−1 photoperiod coupled with a DLI of 14.4 mol m−2·d−1 for the slow growth stage and 17.2 mol m−2·d−1 for the rapid growth stage of hydroponic lettuce cultivation in an LED plant factory. [ABSTRACT FROM AUTHOR]

To rapidly produce strawberry (Fragaria × ananassa Duch. cv. Benihoppe) transplants from cuttings, suitable light intensities for unrooted runner plants at the rooting stage and rooted runner plants at the seedling stage were determined in a plant factory under LED lighting. At the rooting stage, unrooted runner plants at the 3-leaf stage were hydroponically rooted for 6 days under light intensity of 30, 90, 150, and 210 μmol m−2 s−1, respectively. At the seedling stage, rooted runner plants were hydroponically grown for 18 days under light intensity of 90, 180, 270, and 360 μmol m−2 s−1, respectively. The tube LED lights consisting of white and red LED chips were used as sole light source, and photoperiod was controlled as 16 h d−1. The results showed that the maximum root number (7.7) and longest root length (14.8 cm) of the runner plants were found under 90 μmol m−2 s−1 at the rooting stage. Photosynthetic activity in runner plant leaves under 90 μmol m−2 s−1 were higher than that under 30, 150, and 210 μmol m−2 s−1. Higher light intensity at the range of 90–270 μmol m−2 s−1 increased the stomatal conductance of newly formed leaves of rooted runner plants, thus improving the net photosynthetic rate and growth of rooted runner plants at the seedling stage. The crown diameter, shoot and root dry weights, and root to shoot ratio of rooted runner plants increased by 9.7%, 38.8%, 106.1%, and 48.7%, respectively, when the light intensity increased from 90 to 270 μmol m−2 s−1. However, there was no further improvement of runner plant growth under 360 μmol m−2 s−1. Furthermore, no significant difference of increased dry biomass per mole of photons delivered was found between 180 and 270 μmol m−2 s−1. In consideration of transplant quality and economic balance, light intensity of 90 μmol m−2 s−1 at the rooting stage and 270 μmol m−2 s−1 at the seedling stage were suggested for rapidly producing hydroponic strawberry transplants based on unrooted runner plants in the LED plant factory. [ABSTRACT FROM AUTHOR]