Plant physiology and development, ranging from leaf growth and flowering time in Arabidopsis thaliana to tuberization in potato, are profoundly influenced by ambient light con-ditions. It has been acknowledged that light significantly inhibits hypocotyl elongation. However, how light patterns affect early seedling development remains unclear. To ad-dress this, we developed a logistic model for Arabidopsis thaliana hypocotyl elongation. The model incorporated the circadian clock and the PHYTOCHROME-INTERACTING FAC-TOR (PIF)-mediated signaling pathways, capturing the biological characteristics of limited hypocotyl growth. Through numerical simulations, we identified several artificial photoperiods that can accelerate hypocotyl elongation, and thereby promote rapid growth. Compared with the conventional 12L:12D (12 h light/12 h dark) photoperiod, inserting a 4-h light pulse into the dark phase of an 8L:16D cycle advanced the elongation-rate peak by 5.5 h and shortened the growth cycle by 32%. Furthermore, under a 9L:9D photoperi-odic stress, the growth peak occurs 6 h earlier, and the growth cycle is shortened by 25%. These findings highlight the potential role of artificial photoperiods in promoting hypo-cotyl elongation, providing a potential strategy for light control of plant photomorpho-genesis and development.

Light–dark cycles regulate hypocotyl elongation in Arabidopsis thaliana through the circadian clock and PHYTOCHROME-INTERACTING FACTORs (PIFs), but the quantitative relationship between photoperiodic patterns, PIF4/PIF5 dynamics, and growth remains unclear. Here, we modified the circadian-clock-regulated hypocotyl elongation model by integrating a previously established Arabidopsis clock framework with PIF4/PIF5 regulatory interactions and a saturation term in the growth equation. Mathematical properties (existence, uniqueness, non-negativity and boundedness) of the model were analyzed. The model was parameterized using published PIF4 expression and hypocotyl growth datasets and evaluated against photoperiod-dependent PIF4 expression, hypocotyl length responses, and growth dynamics in wild-type and clock- or PIF4-related genetic backgrounds. The modified growth equation captured the saturating nature of hypocotyl elongation under constant darkness (DD), while simulations showed that shorter photoperiods enhance nighttime PIF4/PIF5 protein accumulation and increase hypocotyl growth rates. Bifurcation analysis indicated that sufficient expression of PSEUDO-RESPONSE REGULATOR 5 (PRR5)/TIMING OF CAB EXPRESSION 1 (TOC1) is required to induce PIF4/PIF5 transcript oscillations under the DD condition. The model further predicted that, compared with the 12 h light/12 h dark (12L:12D) condition, the 5L:5D:7L:7D and 6L:5D:6L:7D photoperiod regimes reduced the growth cycle by 23.74% and 22.18%, respectively. This framework serves as a quantitative tool for dissecting photoperiod-dependent hypocotyl elongation and screening optimized artificial light strategies.