Light has properties that can be used for determining particle size and particle size distributions. In the case of diffraction instruments, such as the Microtrac S3500, the angle at which the light is diffracted depends upon the wavelength of the light and the particle size. The angle of diffraction is measured to determine size. For a particular particle size, 首ld the wavelength change, the angle will change. There is another feature of light that can be used for determining the particle size it is the frequency. Frequency is a measure of how many waves pass through a given point during one second. The more waves that cross the point or the closer the distance between the waves, the higher the frequency. Frequency change or shift information is used in Dynamic Light Scattering.