Numerical simulation of light-driven collective motion inspired by experimental observations

Understanding how external stimuli influence collective motion is essential for modeling biological systems and designing artificial swarms. Inspired by a recent experimental study conducted at Université Paris Cité, in which a school of fish responds collectively to a moving luminous stimulus, we develop a numerical model to reproduce these observed dynamics. The particles in our model are attracted to the light source, repelled from each other to avoid collisions, and subject to stochastic fluctuations modulated by the light intensity. By adjusting illuminance over time, our simulations successfully replicate key experimental findings, including the transition from disordered to ordered motion, the formation of cohesive groups, and the emergence of high polarization under strong light. We analyze polarization and average speed over time and demonstrate that the collective behavior undergoes a light-induced phase transition. Our results show strong agreement with experimental data and provide insight into the mechanisms governing collective response to dynamic environmental cues.