by Augustin Fresnel of France and introduced in 1822, the
Fresnel lens signaled the arrival of the golden age of lighthouses.
Through a sophisticated arrangement of prisms, the Fresnel
lens focuses light into a concentrated beam that, in some
cases, could be seen from more than 20 miles away. Designed
in a series of seven sizes (called orders, 1st through 6th,
with a three-and-a-half order), the Fresnel lens could accommodate
a variety of lighthouse sizes and functions. A sixth-order
lens was the smallest in size and therefore had the smallest
focal distance, while a first-order lens was the largest and,
in some cases, reached a height of up to 12 feet. Though he
died only five years after inventing the lens, Augustin Fresnel's
contribution to the lighthouse was, and still is, utilized
to a great extent. From wood fires and candles to oil lamps
and incandescent bulbs, no technological advance contributed
more significantly to lighthouses than the Fresnel lens.