The Bodie Island and Ocracoke Lighthouses have a long and fascinating history, but their familiar beacons will be missing from the nighttime views at Cape Hatteras National Seashore beginning September 28. Fear not, they'll both be back after renovation work is completed.

The current Bodie Island Lighthouse went into service in 1872, the third such beacon in the vicinity, so it's understandable that a bit of rehab is needed. The structure has fared much better than its two predecessors; the first light at Bodie Island was constructed in 1847, began leaning only two years later, and had to be abandoned in 1859.

Bodie Island Light version 2.0 was completed in 1859, but had a much shorter history and a violent demise. Fearing that the 80-foot tower would be used by Union forces, retreating Confederate troops blew it up in 1861.

Work on a replacement light at Bodie Island didn't begin until 1871, spurred by "numerous petitions from concerned ship captains." They had ample cause for worry. According to a park publication,

In 1837, the federal government sent Lieutenant Napoleon L. Coste of the revenue cutter Campbell to examine the coastline for potential lighthouse sites that would supplement the existing one at Cape Hatteras. Coste determined that southbound ships were in great need of a beacon on or near Bodie Island …“more vessels are lost there than on any other part of our coast.”

The current Bodie Island Lighthouse features one of the few remaining original examples of a first-order Fresnel lens. Manufactured in 1871 by Barbier & Fenestre in Paris, France, the huge lens has an inside diameter of 6 feet, 9/16 inches.

Serious lighthouse buffs understand the significance of those facts, but for the rest of us, here's the essential information about Fresnel lenses from a park publication:

"…one of the greatest improvements in lighthouse technology came in 1822 when a French physicist named Augustin Jean Fresnel (Freh-nel) introduced a new lens design that would revolutionize lighthouse optics and make waterways safer for sailors around the world.

Fresnel’s lens resembles a giant beehive with a complex system of multi-faceted glass prisms mounted in a brass framework. The prisms reflect and refract (bend) light and magnify it, thereby taking rays of light that would normally scatter in all directions and focusing them into a single beam.

This concentrated light of Fresnel’s lens vastly improved lighthouse effectiveness. Before its invention, the brightest lighthouse beams could only be seen from 8-12 miles away. The light from a Fresnel lens could shine all the way to the horizon, more than 20 miles away.

Fresnel lenses are divided into different sizes, called "orders," and here's why the lens at Bodie Island is especially significant:

The first order lens is the largest and most powerful. It can be 12 feet in height and more than 6 feet in diameter. Used primarily as a seacoast light, its beam is visible over twenty miles out to sea. The sixth order is the smallest lens, being only about one foot wide and used in harbors and channels.

Here's a bit of historical trivia that can help qualify you as a lighthouse expert: Although the numbering classification for Fresnel lenses goes from first to sixth, there are actually seven sizes of lenses on the current Fresnel scale, which includes a "Third and 1/2" order lens" in the middle of the list.

Two Fresnel lenses are still in use at Cape Hatteras National Seashore.

The Ocracoke Island Lighthouse has a fourth order lens that produces a solid, steady light visible for 14 miles. The Bodie Island Lighthouse has a first order Fresnel lens with an interesting flash pattern. The light is on for 2.5 seconds, off for 2.5 seconds, on for 2.5 seconds, and then off for 22.5 seconds.

The Cape Hatteras Lighthouse’s first order Fresnel lens was damaged by vandals and had to be replaced with an aerobeacon that flashes every 7.5 seconds.

The work on the Bodie Island Lighthouse, which is expected to take at least 18 months, will include:

• removal of the 344 glass prisms for cleaning;
• cleaning and restoration-in-place of the metal panels that hold the prisms and of the metal pedestal that supports the lens;
• Strengthening the support of 10 flights of the lighthouse’s spiral staircase and replacement of 21 cracked stair treads;
• Removal of lead paint and repainting the lighthouse interior;
• Electrical work and installation of a fire detection and suppression system.

The second upcoming project involves the Ocracoke Lighthouse; constructed in 1823, it's the oldest operating lighthouse in North Carolina. Ocracoke Inlet was once one of the busiest inlets on the East Coast, and it achieved early notoriety: it was first placed on maps after English explorers wrecked a sailing ship there in 1585.

The present lighthouse stands about 75 feet tall and its diameter narrows from 25 feet at the base to 12 feet at its peak. The solid brick walls are 5 feet thick at the bottom tapering to 2 feet at the top, and are crowned by an octagonal lantern. Originally an oil-burning light, the Ocracoke Light was electrified in the early decades of the 1900s. Its fourth-order Fresnel lens was installed in 1854 and casts a stationary beam that can be seen 14 miles at sea.

Renovation work at the Ocracoke Lighthouse will take about four months. The lens will remain in place but be temporarily extinguished and protected while work is underway. The project includes renovation of metal work on the interior and exterior, painting of the lighthouse interior and repairs to the lightning protection measures take place.

Past experience at Ocracoke confirms that lightning protection systems are important features for lighthouses. The first lighthouse serving Ocracoke Inlet, a wooden, pyramid-shaped tower constructed in 1798, was destroyed by fire after it was struck by lightning in 1818.

What impact will turning off the lights at Ocracoke and Bodie Island have on mariners? The lighthouses still function as navigational aids, although most present-day captains rely primarily upon electronic tools rather than visual cues. If you're a recreational boater and depend upon these lights for safe travel, you need to be aware of the upcoming work.

A "Broadcast Notice to Mariners" will be issued by the U.S. Coast Guard concerning the temporary interruption of the lights and will provide updates to mariners until the lights return to normal operations.

If you’re interested in climbing to the top of a lighthouse at Cape Hatteras, your destination needs to be the Cape Hatteras Lighthouse, but don't wait too long. The "climbing season" for that tower ends for the year on Monday, October 12. Click here for hours and dates of operation and more details about the tallest lighthouse in North America.

Driving directions, maps and other information to help you plan a visit to Cape Hatteras National Seashore are available on the park's website.