Tyndall effect

The Tyndall effect is when light is scattered by particles of matter in its path. It makes a beam of light visible by lighting the particles.
Under the Tyndall effect, the longer-wavelength light is more transmitted while the shorter-wavelength light is more reflected by scattering. In effect, blue light is scattered much more strongly than red light.
The blue of a clear sky, and the blue of blue eyes is caused by the Tyndall effect, not by a pigment. Its named after John Tyndall. 
Tyndall effect can also be observed when sunlight passes through the canopy of a dense forest. 
It happens due to the scattering of light by the particles of smoke and dust.