The Third Order Fresnel Lens Seeing The Light

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Application

The Third Order lens was used in coastal lights which lead the mariner from one point to another along the coast. It also marked sounds, the entrances to rivers, bays, and channels. Three of the Great Lakes lights fitted with this lens were Whitefish Point, Big Bay Point and Au Sable Point.

Specifications
Lens height: 62.05".
Focal length:  19.7"
Weight of assembly:  1,985 lbs.
Relative brightness (over sixth order): X3.85
Useful range:  Up to 18 nautical miles.
Number in US Lighthouses in 1884: 49
Number in US Lighthouses in 1922:  65
Oil consumption per hour 7 0z.

References

Annual Report of the Lighthouse Board, 1884
The United States Lighthouse Service
, Dept of Commerce, 1915
Aids to Navigation Manual, US Coast Guard, 1945
Comparative Table of Lens Orders, Mabel A. Baiges, 1988
Letter from Al & Helen Gademsky, 07/02/01

Terry Pepper. This page updated 12/02/2007

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