Nocturnal animals can be harmed by light pollution because they are biologically evolved to be dependent on an environment with a certain number of hours of uninterrupted daytime and nighttime. The over-illumination of the night sky is affecting these organisms (especially birds).
Dark-sky preserves like the Great Sand Dunes National Park & Preserve are the main contributors to the dark-sky movement. They are protected areas found mostly in national parks that have a zero light pollution policy set in by the government and controlled by the National Dark Sky Association.