The Light

Q. What fueled the original light?
The original light was Argand style lamps mounted in front of parabolic reflectors. In 1839, Cape Hatteras was fitted with eighteen 14” reflectors. By 1849, the light had been upgraded to fifteen 21” reflectors. This system used whale oil for fuel and, if in perfect operating condition, produced a medium intensity light that could be seen up to 20 miles.

The first order Fresnel lens, installed in 1854, initially burned whale oil as well. However, due to over-hunting, the Sperm whale was becoming scarce and, by the 1870s, the Service was in need of alternate fuels. There is no known record of exactly when the last whale oil was used in a US lighthouse but it is still mentioned in the 1871 Instructions to Light-Keepers along with colza (wild cabbage or rapeseed) oil. Colza oil was one of the replacements that the service considered but it was difficult to get because it was a low profit crop for US farmers. By 1880, whale oil had disappeared from the scene and, according to the 1881 Instructions to Light-Keepers, the available fuels were lard oil and mineral oil (kerosene). There was a very short experiment at Cape Hatteras using porpoise oil. It was found to be totally unacceptable and was not adopted. From 1913 to 1934, the light was provided by an incandescent oil vapor (IOV) lamp using pressurized kerosene in a mantle, similar in operation to the modern Coleman lamp used for camping. Official records show that kerosene still fueled the Cape Hatteras light as late 1927.

Q. What was the original optic in the 1870 tower?
Like most late 19th century lighthouses, this one used a Fresnel lens. Fresnel lenses were manufactured in a series of sizes or orders with first order being the largest, over 17 times as powerful as the smallest (6th order). In this case, over 1,000 prisms were used and, all told, about 2,500 lb. of glass and bronze made up the 12 foot tall first order assembly. Triangular prisms projected light into a continuous 360 degree beam, and, in this case, 24 bulls-eye lenses provided the flashes. The light has always been white; at other lighthouses, red and green have also been used (mainly harbor and range lights because color reduces the range of the beam).

Q. What machine turned the first order Fresnel lens?
The original lens assembly, which rotated on a chariot at ½ rpm, was turned by three 150 pound iron weights suspended on a cable and dropping down the center. The cable was wound around a drum in the clockwork mechanism beneath the lens, which worked much like a grandfather clock. Each morning, the weights were slowly cranked by hand to the top and then released at dusk when the lamp was lit, causing the lens to rotate. The gears in the mechanism provided the leverage to turn the 1-½ ton lamp/lens assembly. The speed of rotation could be adjusted by a fan governor in the clockwork. A gentle hand push was used to start the lens rotating but, once it was in motion, it maintained its rotation until the weight reached the bottom of the tower and had to be rewound. Regulations required that the weight be rewound to the top of the tower every morning. In many shorter lighthouses, cranking was needed every few hours.

Q. Does the lamp flash?
No, it rotates, like an airport beacon. The 'flash' is visible when the beacon points at you. The original Fresnel lens system cast 24 beams, the current beacon projects two.

Q. How far away is it visible?
The official range is 24 nautical miles (a nautical mile is 6,080 feet). At night, most vessels in clear weather can see the lighthouse from up to 20 nautical miles at sea. Seen exactly at sea level, the direct visible range is about 15.6 nautical miles. The USLHS standard was to allow an extra ten feet of height to account for the height of the bridge deck, giving 16.2 miles. At night, the glow or loom can be seen when the light is actually below the horizon; in some atmospheric conditions refraction causes the light to follow the earth's curvature, too. These phenomena are also factored in. The range of the lighthouse depends more on height and air clarity than on the power of its beacon.

Q. What is the current optic and how powerful is it?
Two separate units, similar to search lights, are mounted side by side facing in opposite directions, and are turned by an electric motor. The beacon is controlled by a photocell, which automatically turns the light on at sunset and off at dawn. Each 1,000- watt bulb (120 volts - same as your house), less than 10 inches tall, puts out an 800,000-candlepower beam focused by two parabolic reflectors. A spare bulb and primary reflector automatically rotate into place when the primary bulb burns out. GE makes the bulbs. They are halogen/argon filled, with a tungsten filament, and cost about $240 each. The mechanism is similar to an airport beacon.

Q. When was the light electrified?
In 1934, shortly before the light was moved to the tower in Buxton. A 36-inch (nominal) airport beacon was originally used. The current 24-inch (nominal) beacon, type DCB (Directionally Coded Beacon) 224, was installed in 1982.

Prior to the installation of the airport beacon, the Fresnel lens only used electricity for the light source but still used the clockwork and weight system to turn the optic.

Q. Is there another lighthouse on the Diamond Shoals?
Not any longer. In 1968, a “Texas Tower” light station, a structure similar to an offshore oil rig, was completed out on the Diamond Shoals. The light was located approximately 12.8 nautical miles or 14.7 statute miles out in the Atlantic Ocean. It was originally crewed by 6 people (4 on and 2 off) but was automated on September 7, 1977. The 1000-watt lamp was 125 feet above the water and was visible 22 nautical miles. The Diamond Shoals Light Station was de-commissioned in 2002 and the light is no longer operational.

Last updated: April 14, 2015

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