Doppler effect is applicable for light as well as sound waves. 

Most people get confused about the applicability of the doppler effect in light waves. 

Doppler effect is applicable while we are waiting for a bus, an ambulance passes us by. We listen to the diminishing sound of the siren while it goes away from us.

In Medicine, doctors use the doppler principle by using an echocardiogram to analyze blood flow velocity at any particular time.

In submarines, the doppler effect is used to calculate the speed 

In astronomy, the speed of galaxies and stars is estimated by using the doppler principle.