The VRB-25 is a lighthouse

Lighthouse

A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....

 optical system designed and built by Vega Industries

Vega Industries

Vega Industries Limited is a company in Porirua, New Zealand which manufactures specialized navigation and signal lights for use in transportation industries, primarily marine navigation. Vega has been in business since 1972...

 Ltd. in Porirua

Porirua

Porirua is a city in the Wellington Region of New Zealand, immediately north of the city of Wellington, with their central business districts 20 km apart. A large proportion of the population commutes to Wellington, so it may be considered a satellite city. It almost completely surrounds...

, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. It was originally designed in 1993-95 with the assistance of the United States Coast Guard

United States Coast Guard

The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...

 to meet USCG requirements for a robust mechanism requiring minimum maintenance. It has become the Coast Guard's standard 12 volt rotating beacon. The company's literature says there are more than 400 installations worldwide. More than a quarter of the active lighthouses in Maine have one installed.

Components

A microprocessor controlled 12 volt DC motor drives an array of six or eight acrylic Fresnel lens

Fresnel lens

A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...

es around a bulb at one of 248 speeds ranging from 0.5 to 15.9 revolutions per minute (RPM). In the simplest case, all six lenses are used, so that for Boon Island Light

Boon Island Light

Boon Island Light is located on the 300x700 foot Boon Island off the southern coast of Maine, United States, near Cape Neddick. Boon Island Light has the distinction of being the tallest lighthouse in both Maine and New England at 133 feet. The lighthouse has a focal plane at 137 feet above mean...

, which shows one flash every five seconds, the mechanism rotates at two RPM. Eight lenses are used only when required to achieve more complex characteristics.

Maximum range is achieved by using the slowest possible speed, but for grouped flashes, it is necessary to blank off lenses and rotate the mechanism faster. So, for example, for The Cuckolds Light

The Cuckolds Light

The Cuckolds Light is a lighthouse in Boothbay Harbor, Maine.It was first established as a daymark. In 1892 a fog signal was added and the current structure was built in 1907....

, whose characteristic is group flashing two every six seconds, all but two of the six panels are blanked off and the mechanism rotates at ten RPM.

The mechanism is driven by a DC thirty-pole three phase brushless direct drive motor which consumes approximately 1.5 watts. The microprocessor controller keeps the motor speed within 2% of that chosen through feedback from an alternating black and silver circle on the bottom of the turntable. The unit is designed to accept voltages ranging from 11 to 30 Volts. Since the life of an incandescent

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

 lamp decreases dramatically as the applied voltage increases, the lamp voltage is carefully maintained at 12.00V using pulse width modulation.

The lamps, standard marine signal lamps which may be from 10 to 100 watts as required to produce the necessary range, typically have a life of 2,000 hours. The unit contains a bulb changing mechanism which holds six bulbs, so that a unit could go approximately three years between maintenance visits to change bulbs. The acrylic lenses and cylinder surrounding the whole mechanism are designed to be UV

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 resistant, but still require replacement approximately every five years. In practice, since working lights are critical to navigation, the Coast Guard actually services lights more frequently. Except for that maintenance, the unit is expected to last twenty years.

Predecessors and Successors

LED

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

 lamps are beginning to replace incandescent lamps in lighthouse applications, so it seems likely that the twenty year replacement will be with an LED light source. In fact, several VLB-44 LED beacons, also made by Vega Industries, have been installed by the USCG, including one at White Island Light.

From the first use of lighthouses with flashing lights, the light source has been continuous. Turning a flame on and off was impractical and flashing an incandescent electric lamp reduces its life substantially. The characteristic seen by the observer has been achieved by rotating a lens system. Since LEDs can be flashed on and off without degrading their lives, it appears that the VRB-25 is the last use of rotating beacons in lighthouses.

Issues

Although the units have been successful in their adoption, there has been occasional controversy (at Egg Rock Light

Egg Rock Light

Egg Rock Light is a lighthouse on Frenchman Bay, Maine.It was established in 1875. The structure is unusual—the brick light tower is in the middle of the white wood frame keeper's house....

, for example) when the Coast Guard has removed the lantern from the tower after installing a VRB-25. This seemed logical since the lantern required maintenance and the VRB-25 is designed to sit outside, but it changed the traditional look of the towers. All the VRB-25s listed below, except Piedras Blancas, still have lanterns.

While the beam is visible at its listed range, it is a more focused beam than that produced by a glass Fresnel lens. Some navigators don't like this, finding it harder to see under some conditions. It is easy to see the difference from many points around Boston Harbor, where the VRB-25 at The Graves Light and the 2nd order glass Fresnel lens at Boston Light

Boston Light

Boston Light is a lighthouse located on Little Brewster Island in outer Boston Harbor, Massachusetts. The first lighthouse to be built on the site dates back to 1716, and was the first lighthouse to be built in what is now the United States...

 are both visible. Of course, the original first order Fresnel lens at The Graves stood twelve feet high and weighed several tons. Its many pieces of glass required periodic careful cleaning and alignment.

Examples of Lights using the VRB-25

Light	Characteristic	Range, nm
De Tour Reef Light, Michigan	Fl W 10s	18
The Graves Light, Massachusetts	Fl W (2)12s	15
Mount Desert Light Mount Desert Light Mount Desert Light is a lighthouse on Mount Desert Rock, a small island about south of Mount Desert Island, and is part of the US state of Maine... , Maine	Fl W 15s	20
Piedras Blancas Light Piedras Blancas Light Piedras Blancas Light Station is a lighthouse on Point Piedras Blancas, about five and half miles west by NW of San Simeon, California.-History:... , California	Fl W 15s	19
Thimble Shoal Light Thimble Shoal Light Thimble Shoal Light is a sparkplug lighthouse in the Virginia portion of Chesapeake Bay, north of the Hampton Roads channel. The third light at this location, it is listed on the National Register of Historic Places.-History:... , Virginia	Fl W 10s	20
West Point Light, Washington	Alt W & R 10s	W 16 and R 13

External links

• Terry Pepper, Seeing the Light "Vega VRB-25 Rotating beacon"