In this thesis, we study the optical model to precisely describe optics and color distribution of the lights emitted by a blue LED covered with silicate phosphors. The optical model starts Mie scattering model and Monte Carlo ray tracing to describe the scattering of the lights when they are propagated in the phosphors, and the ray tracing is performed with blue and yellow rays. Through simulation and experimental measurement, we have successfully built an optical model, which can be applied to decide some package parameters in a white LED and to avoid color dispersion of the light pattern. Besides, we observed some interesting effects such as thermal decay and re-absorption of the phosphors. These effects could limit the validity of the optical model and need more study to make the optical model more correct.