The final stage of coalescence during latex film formation was simulated by using adjacent donor and acceptor cubes. The interdiffusion of the donors and the accepters within these cubes was generated using the Monte-Carlo technique. The delay of the donor intensity I(t) by direct energy transfer (DET) was simulated for several interdiffusion steps; then the I(t) curve was convolved with the experimental profile and Gaussian noise was added to generate realistic time-resolved fluorescence (TRF) data. I(t) decays were fitted to the phenomenological equation to obtain the fractional mixing at each interdiffusion step. These results were compared with real TRF and steady-state fluorescence (SSF) experiments. The reliability of the Fickian diffusion model is discussed for latex film formation.