Why Two Lights?
Two Lighthouses Separated by 320 feet
At the time the first Twin Lights came to be, the U.S. Lighthouse Board believed that lighthouses should have a fixed (non-rotating) light or beacon. There was a concern, however, that vessels might confuse a single light on the Highlands of Navesink with the Sandy Hook Lighthouse (five miles to the north).
The decision was made that the new Navesink Light Station would comprise two lighthouses separated by 320 feet. One tower would have a fixed light and the other would have a rotating light, so that mariners could easily differentiate between the single Sandy Hook Light and the dual lights of the Navesink Light Station.
As the years passed, the Lighthouse Board constructed seven dual or twin lights, and one triple light, following the same philosophy. The high operating expense of these multiple units eventually convinced the board to consider other alternatives. So many lighthouses were being constructed in the 1800s that this fixed-light policy would force the building of dozens of double- and triple-lights. The ultimate solution was to have each lighthouse emit light in its own specific code or pattern. The most famous and well known signaling scheme is the “I Love You” flashes of the Minot’s Ledge Lighthouse off the coast of Cohasset, Massachusetts. The signal flash sequence is actually “flash – flash, flash, flash, flash – flash, flash, flash” or 1, 4, 3 the number of letters of “I Love You”.
In 1898, when the 25 million candlepower Second Order Bivalve Rotating Fresnel Lens was installed in the South Tower of the Twin Lights, the light in the North Tower was no longer needed and reduced to backup status. In 1949, when Navesink Light Station was decommissioned, the South Tower lens was removed and sent to the Lighthouse Depot at St. Georges on Staten Island, New York. In 1951 that lens was loaned to the Boston Museum of Science where it was put on display. In 1979 the Museum of Science returned the lens to the Twin Lights Historic Site, where it is now displayed in the Generator Building.
The South Tower of the Twin Lights is now and will remain permanently unlighted. The lone exception came in June 2008, when it was re-lighted temporarily for the production of a documentary film on the Twin Lights. The North Tower has been lighted since 1981 by a 500 watt bulb from dusk to dawn, as a private aid to navigation.