Dynamic light scattering measures the fluctuation changes in the intensity of scattered light to determine particle size and properties. It works by measuring the rate at which the intensity of scattered light fluctuates due to Brownian motion of particles. Larger particles diffuse more slowly than smaller particles, so intensity fluctuations are slower for large particles. The correlation function contains information about particle diffusion, with steeper curves indicating more monodisperse samples and more extended decay indicating greater polydispersity. Dynamic light scattering can determine particle size distribution, hydrodynamic radius, and diffusion coefficient.