Diurnal changes in solar position plus occlusion caused by overlapping foliage means that throughout a day, leaves alternate between periods where they are either sunlit or shaded. Describing these patterns for real plant canopies is difficult and computationally intensive.
Retkute et al. combine high-resolution reconstructions of field-grown plants with ray-tracing to analyse how light dynamics vary for different plant species, planting densities and leaf area indices. They develop a stochastic model which involves two states, sunlit and shaded, where the rates of switching between states are a function of time of day and the depth within the canopy.
Retkute, R., Townsend, A. J., Murchie, E. H., Jensen, O. E., & Preston, S. P. (2018). Three-dimensional plant architecture and sunlit–shaded patterns: a stochastic model of light dynamics in canopies. Annals of Botany, 122(2), 291–302. https://doi.org/10.1093/aob/mcy067