Fresnel Lenses were designed in two basic styles, fixed and rotating.
The rotating lens is mounted on a pedestal designed to turn the lens at a certain rate of speed.
All style Fresnal lenses have a lamp mounted in the center or focal point of the lens with prisms arranged around the lamp to capture and redirect the light.
Both fixed and rotating lenses have the same 2 dimensional cross section, the difference is how the prisms are shaped 3 dimensonially.
The prisms in a rotating lens are revolved around a horizontal axis through the focal point of the lens, forming concentric rings, also called "bulls eye" lenses.
With the prisms being curved around the focal point of the lens the sheet of light that is projected from the lens follows the same curvature as the prisms forming a focused beam of light.
The prisms are mounted in a brass framework. Each section of prisms between the brass frames is called a flash panel.
This entire panel lights up from top to bottom and side to side.
Each flash panel sends out a beam of light to the horizon.
The signature or characteristic of the lens is determined by the number of flash panels and the speed of rotation.
From in front of the lens and observer would see a flash of light as the panel rotates in their line of sight.
In between each flash panel no light is directed at the observer and is called an eclipse.
From a distance the mariner would see a series of flashes or characteristic that was designed for that particular lighthouse.