The changes in surface flux (irradiance) and actinic flux (radiant energy density) caused by an elevated scattering layer have been computed using radiative perturbation theory, a technique which is well suited to addressing such questions. A range of layer elevations and solar zenith angles was considered, for wavelengths of 300 nm and 550 nm. Our results for 300 nm are in broad agreement with a recently published single-scattering calculation, showing large enhancements when both layer elevation and solar zenith angle are high. Our results for 550 nm show a somewhat unexpected enhancement in actinic flux for small solar zenith angles. ¿ American Geophysical Union 1995