The capability of diffraction intensity fluctuations to probe dynamic phenomena at equilibrium is studied. The summation of fluctuations over different domains that scatter incoherently, the role of statistically “white-noise” generated fluctuations and the time necessary to collect a sufficiently long signal are investigated. The factors that determine the number of incoherent regions, and maximize the relative fluctuation without reducing the count rate to such low values that impractically long acquisition times are needed are discussed. Monte Carlo simulations modeling thermally generated step fluctuations are used to illustrate the results. ©1997 American Institute of Physics.