For Low Light Level E/O systems, the Air Light may give the major part of a signal, but will reduce the possible resolution. Photographic envelope, defined for different imaging systems applications, must include such effects. The scattering and absorption of sunlight by atmospheric aerosols, molecules and ozone affects the quality of images and is usually described in terms of a Multiple Scattered Radiation. Such radiation, responsible for creating Air Light, is a complicated physical and computational problem, that sometimes gives very untrivial results. This paper reviews the atmospheric path radiance Air Light as a part of a system approach to E/O systems. We present the algorithm for calculation of many stage scattering processes and suggest a non sophisticated criterion for its importance.