In this paper we investigate the scattering of a two-level atom in a traveling or standing wave in the limit of large detuning. We show that these two systems are examples of nontrivial motion which is straightforward to treat using the unified scattering formalism of Tanguy and co-workers [J. Phys. B 17, 4623 (1984)]. This enables us to compare the diffractive and diffusive approximations with the exact solution of the effective master equation. Our analysis is fully quantum mechanical and in our numerical treatment of the effective master equation we are able to include spontaneous emission to all orders. We find that whereas the diffractive approximation correctly describes scattering from a traveling and a standing wave for short interaction times, the diffusive approximation cannot account for the persistence of diffractive structure for the case of the standing wave. To get good agreement we use an approximation which incorporates both diffractive and diffusive effects.