Atoms and other particles inevitably scatter some of the light that hits them. The light isn’t absorbed, just sent in another direction in a process called Rayleigh scattering, after the British physicist Lord Rayleigh, as shown in Figure below. However, the distinction between scattering and absorption doesn’t matter much if you are trying to send light through a fiber, because the light is lost from the fiber in either case.

Like absorption, scattering is uniform and cumulative. The farther the light travels through a material, the more likely scattering is to occur. The relationship is the same as for light absorption, but the fraction of scattered light is written S.

Scattering depends not on the specific type of material but on the size of the particles relative to the wavelength of light. The closer the wavelength is to the particle size, the more scattering. In fact, the amount of scattering increases quite rapidly as the wavelength X decreases. For a transparent solid, the scattering loss in decibels per kilometer is given by