To better advise you it might be good if you could post the work you've done now or any examples of similar lighthouse animations; I can imagine there are many different views (top-down, 3D, etc.) on this.
One thing that might be a cool effect is incorporating the use of Hype's Backdrop Filter Effects. These could be made to increase the brightness of objects the light is shining on.
Another technique would be to use shapes that are black and partially transparent in the foreground to make everything but the lit area dark.