This article will give an overview of all effects that determine the spectral features amplitude (SFA). The origin of spectral features is explained and methods are indicated that can be used to minimize the SFA. Spectral features are observed in the ratio between two spectra of sun calibration measurements. Mechanisms helping to reduce spectral features are spectral averaging, angular averaging, and temporal averaging. It will be shown what optical design choices can be made in order to benefit from these SFA reducing mechanisms. In the final chapter some insight in the modeling is given where four types of diffusers are compared. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).