Bragg reflection amplitudes are examined for the structures P, D, G, C(P), C(D), I-WP, and F-RD in amphiphilic systems. For these ordered phases, a very simple analytical formula for the scattering amplitudes is given. The formula allows determination of the scattering amplitudes for any cross-sectional density profile of the membrane decorating the minimal surface. Within this approximation an analytical solution for the Debye-Waller factor is presented. Finally we propose a simplified model that can greatly facilitate examination of the experimental scattering patterns.