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Lighting Technology and Fuels
 Three factors have determined how far the Copper Harbor light shines: weather, the
light's height and its intensity. Improvements in fuels and lighting technology have
increased the light's intensity over the years.
Its entry is indicated by a beacon of which the flame can be seen during the night a
distance of 6-7 kilometers.
(M. L. E. Rivot, Traveler, 1855)
The first Copper Harbor light tower was equipped with 13 Argand lamps and reflectors
mounted on a stationary frame called a chandelier. Each lamp had a hollow circular wick
that burned with little smoke and a parabolic (bowl-like) reflector behind it that
intensified the light and directed it toward the horizon. The initial fuel was whale oil,
which was replaced by less expensive lard oil in the 1850s. This light could be seen at a
distance of four miles.
Fresnel lenses, used at Copper Harbor from 1856 until 1937, were perfected by French
physicist Augustin Fresnel. The Fresnel lens used glass prisms and a powerful magnifying
glass to refract (bend) the light of a single lamp into an intense beam. It came in seven
orders (sizes); the first order lens was the largest. The light in the background of the
exhibit photograph is a fifth order lens; the light in the foreground is an auxiliary
light formerly used at Copper Harbor.
The government installed a sixth order Fresnel lens at Copper Harbor in 1856. It
replaced it in 1859 with a larger fourth order lens, which was used until the steel tower
was constructed in 1933. Improved lighting technology, such as the changes in fuels shown
in the chart below, increased the visibility of the Copper Harbor light. It could be seen
from ten miles away in 1869 and from 15 miles away in 1907.
The automated acetylene-fueled light installed in the lighthouse in 1919 was moved to a
60-foot-high steel tower in 1933. In 1937, a battery-operated beacon replaced it on the
tower. The beacon stands 90 feet above the waters of Lake Superior and can be seen at a
distance of 22 miles. Crews on passing vessels recognize it by the color and interval of
its flashing green light.
Copper Harbor Lights
| Year |
Light |
Fuel |
| 1849 |
Parabolic Reflector |
Whale Oil |
| 1856 |
6th Order Fresnel Lens |
Whale Oil |
| 1859 |
4th Order Fresnel Lens |
Lard Oil |
| 1879 |
4th Order Fresnel Lens |
Mineral Oil (Kerosene) |
| 1919 |
4th Order Fresnel Lens |
Acetylene Gas |
| 1937 |
300 Millimeter Lens |
Electricity |
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