Colloids, also known as colloidal solutions or colloidal systems, are mixtures in which microscopically dispersed insoluble particles of one substance are suspended in another substance. The size of the suspended particles in a colloid can range from 1 to 1000 nanometres (10-9 metres). For a mixture to be classified as a colloid, its suspended particles must not settle (in the manner that the particles of suspensions settle at the bottom of the container if left undisturbed). Colloidal solutions are known to exhibit the Tyndall Effect, which is a phenomenon in which beams of light incident on colloids are scattered due to the interactions between the light and the colloidal particles.