All lighthouses I knew had a rotatory system with a screen creating the "flashing" sequence according to a rythm previously decided. (The dioptric system was a marvel to see).
The light there was always ON.
Perhaps, newest ones have an electronic based system. Have you searched the Web?.
I think what he is asking for is a schematic for making a model lighthouse using the PIC16F876A. I assume he is interesting in a model for a diorama or a model train layout.