Small angle light scattering (SALS) is one of the tools that can be used to study a phase separation. It is shown that SALS can be used to discriminate between nucleation and growth (NG) and spinodal decomposition (SD) even when both give a pattern composed of a ring. To support this, a complete calculation of the light scattering of an NG process is performed, taken into account the correct Mie form factor and adding polydispersity, multiple scattering and non-independent scattering. All these factors are shown to play a role that gives patterns that cannot be confused with the one originating from an SD. (C) 2001 Elsevier Science Ltd. All rights reserved.