Tyndall Effect occurs when light scatters on particles in a colloid system. Colloid is different from liquid and solution, and since Tyndall Effects only occurs in colloid but not either liquid or solution, tyndall effect is useful for identifying colloid from liquid or solution. But by how? Well, if you shoot a light beam ( from flash light, etc) towards a colloid in a beaker, you will see the trace of the light beam going through clearly. But for either a solution or a liquid, this won't happen.  When Tyndall Effect occurs, those light with longer wavelengths can be transmitted through, while those light with shorter wavelength will be reflected via scattering. The sky is blue because blue light has the shortest wavelength for visible light, and it is reflected via scattering all over the place, so the sky has a blue color. In the forest, most of the time we can see light beams coming from the sky because the dirt and other small particles in the air form a colloid system, so light is scatted and form a light beam. In foggy weather, the light from car headlight will also form a light beam through the fog for the same reason.