Split Rock Lighthouse – The Lens

Split Rock is equipped with a 3rd order bi-valve fresnel lens. The lens in the lighthouse was manufactured by Barbierre, Bernard, & Turrene in Paris, France and imported to the United States. It was shipped disassembled in crates and then reassembled in the tower. The lens is composed of 242 glass prisms that are mounted in a brass frame. It has two flash panels, or “bulls-eyes”, that focus the light into two distinct beams. It is mounted to a pedestal that floats in a pool of liquid mercury and the entire lens assembly is rotated by a clockworks. The rotation of the lens causes the two beams of light it produces to sweep across Lake Superior, giving the light the characteristic flash (once every 10 seconds) that identifies it to passing ships.

The Great Eye at Split Rock Light
This photo is taken from the watch room of the lantern, looking up at the lens. It was taken before the 2010 centennial renovation had been done, so you can see the small amount of rust and flaking paint on the roof the lantern, above the lens.

Two Harbors Trip - Fall 2011 - The Lens at Split Rock Lighthouse
This photo was taken after the 2010 centennial restoration was complete. The rust and flaking paint in the previous photo has been repaired and repainted.

Two Harbors Trip - October 2011 - Split Rock Lighthouse - The Lens Manufacturer Plate
This photo shows builder’s plate for the lens, which is still mounted to the pedestal that supports the lens.

Split Rock Lighthouse:  The Beautiful Lens
This photo shows one of the two bulls-eye panel on the lens.

Split Rock Lighthouse:  The Beautiful Lens
This photo shows some of the detail of the prisms mounted in the brass frame.