In reality lighthouses do not emit a beam of light, but a flash of light.
The lens in the lighthouse optic is the only part of lighthouse technology that has not changed for almost 200 years. It is called a Fresnel lense because it was developed by the French physicist Augustin-Jean Fresnel.
The lense focuses, refracts and reflects the light creating a long distance light flash.
Due to GPS navigation, however, lighthouse no longer require the very long ranging lights and these type of lenses are increasingly replaced with smaller light systems.
Every lighthouse flashes a different signal, so that ships are able to distingish the lighthouses. The Baily lighthouse flashes every 30 seconds. The Kish lighthouse visible from the Baily in the distance, flashes every minute and then two times each second.