The Duluth South Pier Light displays a steady green light from a 4th order Fresnel lens.  The lens is believed to be the original lens from the original lighthouse, which dates it to 1877.  This lighthouse replaced the original in 1901.  This building also housed a large fog signal when it was built.  The current fog signal is an electric horn that is located on the gallery outside of the lantern.  It is the small white cylinder to the left of the lantern in this photo.  Also note the new red metal roof that was recently added to this aging structure.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/9197427@N06">Pete Markham</a> from Loretto, USA
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/pmarkham/1768808443/">Duluth South Pier Lighthouse - A Closeup of the Lantern Room</a>