Tyndall effect
The earth atmosphere is a heterogeneous mixture of particles. These particles include smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam become visible. The light reaches us, after being reflected diffusely by these particles. The phenomenon of scattering of light by the colloidal particles gives rise to tyndall effect.
The Tyndall effect is seen when a fine beam of sunlight enters a smoke-filled room through a small hole. Thus, scattering of light makes the particle visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest. Here, tiny water droplets in the mist scatter light.
The colour of the scattered light depends on the size of the scattering particles. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelength. If the size of the scattering particles is large enough, then, the scattered light may even appear white.