The room at the top of a lighthouse tower that houses the Fresnel lens is called the lantern room or lightroom. This space is specifically designed to hold the Fresnel lens and the light source, often with several large glass windows (or panes) that allow the beam of light to shine out in all directions to guide ships.

The lantern room is located at the very top of the lighthouse tower, ensuring that the light has an unobstructed view and can be seen from great distances. In addition to the Fresnel lens, the room also contains mechanisms for rotating the lens (in the case of a flashing lens) and controlling the light's intensity.

 Before the introduction of electricity, the lighthouse had a clockwork mechanism that caused the lens to rotate. 

When Augustin Fresnel created his first revolving lens it was mounted on small (about 5 inch or 12 cm. diameter) wheels.  These wheels acted as roller bearings to support the weight of the lens and to allow it to rotate freely.  Fresnel described the rollers in his first paper in 1822 as:

“This apparatus can easily be turned around its axis on the column by means of rollers, which move upon a circular projection on top of the pedestal.”

Lighthouses use different types of lenses based on their purpose and the effect needed to guide ships safely. The three major types of lenses are:

Fixed: The light remains constant, without blinking or flashing.

Flashing: The light alternates between bright flashes and periods of darkness. These are the most effective and powerful, as they can be seen from great distances.

Combination of Fixed and Flashing: This type combines a steady light with a flashing light, often to help differentiate between different lighthouses.

Augustin Fresnel's original flashing lens was indeed a revolutionary development. It was designed to rotate and produce beams of concentrated light. Fresnel's lens included bull's-eye panels, which focused the light into powerful beams. For example, an eight-panel Fresnel lens would create eight separate beams of light, and as the lens rotated, these beams would pass across the horizon. This rotation made the light appear as a flash, followed by darkness, which was crucial for mariners to identify the lighthouse from a distance.

Resource Kits

Object Library

Museums

Standards for Parts of the Lens

College, Career, and Civic Life (C3) Framework