This technique is usually used to measure particle size of materials in the submicron region down to below 1nm. Particles that are in suspension undergo Brownian motion caused by thermally induced collisions between solvent molecules and the material particles. When the particles are illuminated with a laser, the intensity of the scattered light fluctuates over time at a rate dependent upon the particle size; smaller particles are displaced further by the solvent molecules and move more rapidly. Analysis of these intensity fluctuations yields the velocity of the Brownian motion and hence the particle size using the Stokes-Einstein relationship. The diameter measured in Dynamic Light Scattering is called the hydrodynamic diameter and refers to the way a particle diffuses within a fluid.