Scattered light is emitted from scattering objects in dispersion. The Brownian motion of the scattering objects produces intensity fluctuations in the signal. Analysis of these fluctuations using the correlation function yields the diffusion coefficient or the hydrodynamic radius (using the Stokes-Einstein equation) of the objects. Small molecules diffuse quickly and produce a fast decay in the correlation function, larger particles diffuse more slowly. The decay rate of the correlation function is related to the z-average particle size. A multi-exponential analysis can produce a size distribution, providing insight into the presence of different species inside a sample. DLS is non-invasive, highly sensitive and requires very little sample volume.