We develop a formulation allowing construction of various kinetic domains from a master equation for population transfer dynamics and enabling calculation of the time scales of transition between such domains. In this way, a complicated network of energy transfer steps can be simplified to a series of sequential kinetic transitions over the kinetic domains. We illustrate the advantage of this formulation by applying it to energy trapping in a photosynthetic light harvesting system and as a result we obtain a clear picture of energy transfer dynamics and the various rate determining steps in Photosystem I. (C) 2003 American Institute of Physics.