Dynamic light scattering (DLS) is a physics technique used for characterizing the size of particles and molecules in suspension and solution. The technique is based on the measurement of the time-dependent fluctuations in the intensity of the scattered light signals. The particles are responsible for the scattering of the light, while it is the random motion of the particles that produces the fluctuations in that scattering. By measuring the scattering, the particles' velocity can be derived, and from that velocity the hydrodynamic diameter of the particles can be calculated by using the Stokes–Einstein equation.