Question

What is the difference between the doppler effect for sound and for light?

Answer 1

They both are same and it doesn't differ.

If the emitting source moves towards/away from a stationary observer, the observer receives more/less‘waves’ per time unit than those emitted by the source.

Sound: The observer hears a higher/lower pitch than what is emitted.

Light: The observer sees a light violet shifted/red shifted in relation to the light emitted.

The Doppler effect is in both cases the same.

For the Doppler effect to be perceptible, the speed of the moving source must of course be in an appropriate relation to the speed of propagation.

For example, a honking car approaching with, say 100 km/hr (36 m/s) produces a very audible Doppler effect, because 36 m/s is a substantial fraction (> 10%) of the 340 m/s of the speed of sound.

To observe an analogous effect with a light emitting source, that source should be approaching (or receding) with over 30 000 km/s, (10% of the speed of light), and this is why we mostly observe this with astronomical objects.