Photo-induced electronic excitations of poly(p-phenylenevinylene) (PPV) aggregates are simulated and characterized using a recently developed linear-scaling localized-density-matrix (LDM) method. The intra- and inter-chain components of excitations are analyzed and quantified for different inter-chain distances. The excitations for the absorption and luminescence in PPV film and its derivatives are identified and are found analogous to those of H-aggregates. Their energy shifts upon aggregation are determined mainly by the inter-chain kinetic energy reduction and the Coulomb interaction of the electron-hole pair. It is concluded that the luminescence is caused by the intra-chain electron-hole pairs.