Lighting Boston Harbor for 150 Years

Lighting Boston Harbor for 150 Years
December 21, 2009
U.S. Coast Guard|by Sally Snowman

One-hundred and fifty-years ago, at sunset on the winter solstice, Boston Light's newly installed second order classical Fresnel lens was lit for the first time on the country's first lighthouse.

The lighthouse, situated on Little Brewster Island at the entrance of Boston Harbor, was built in 1716 to guide ships in safely transiting into the outer harbor. With technological advancements, the most effective lamp device available in the world was installed at Boston Light in 1859. It's a flashing mechanism is comprised of 4,000 pounds of brass and glass rotating on a clock-works mechanism.

The inventor credited for revolutionizing illumination optics in the 1820's was Augustin Fresnel from France. This technology was adopted for use in lighthouses and the U.S. began importing these lenses in the 1840's.

Boston Light's entire assembly is 11 feet tall comprising of 336 individual prisms with 12 bullseyes. Today, the illuminate in the center of the lens is a 1,000 watt lamp, magnifying the light 2,000,000 candle power that's visible for 27 nautical miles on a clear night.

The lighting characteristic is distinguishable from other lights in the harbor with its one flash every 10 seconds. The lamp appears to only flash, but in actuality, the rotation of the lens mechanism allows the bullseyes to capture the light from the 1,000 watt lamp, sending 12 beams of light across the bay appearing as one solid flash of light.


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