A novel formulation of radiation from a localized line source placed in photonic crystals composed of periodic arrays of circular cylinders is proposed. The method employs the spectral domain approach. The spectral response of the photonic crystals to the line source excitation is efficiently calculated using the Lattice Sums technique, T-matrix approach and the generalized reflection and transmission matrices. Radiated field in the far-zone is numerically studied. The physical insight into how the radiation pattern is modified in the presence of the photonic crystals is given based on the theoretical studies.