Abstract: A mathematical model was introduced to describe the vertical distribution of leaf area densities of tea, wheat, and cinnamon canopies and it fitted the data very well although their patterns are considerably different. Therefore, this model is theoretically significant. Leaf declination angles of tea, with a great covariance, tend to be a normal distribution. Radiation regimes vary notably in different canopies; however, light conditions in the lower part of the canopies are the best around noon when extinct coefficient is the smallest. The extinct coefficients being greater for photosynthetically active radiation (PAR) than those for total radiation (TSR) are closely related to the inverse proportion of solar altitudes (sinh0) during one day. Consequantly, under rational consideration of daily variation of the extinct coefficients, traditional exponentially extinguishing relationship is still a good mathematical model for describing radiation regimes within plant canopies with the advantages of being simple, practical, and trustworthy.