Fresnel lenses are classified by size in a series of "orders." The largest is the 1st order lens, which is 8.5 feet high, 6.5 feet in diameter, and weighs 12,800 pounds. The smallest is the 6th order lens. Later, smaller sizes were added, but the original classifications developed by Fresnel remain the standard.
Fresnel lenses are extremely valuable, almost impossible to replace or repair, and their cleaning and maintenance are very labor intensive. For this reason, most of the Fresnel lenses in the United States have been removed from lighthouses and many are preserved in museums.
Today, only one1st order lens remains in service on the East coast north of Virginia. Located at Sequin Island lighthouse near Boothbay, Maine, that lens is valued at over $8 million and recent attempts by the U.S. Coast Guard to replace the lens with a rotating beacon were postponed by public opinion.