VLB-44

The VRB-25 is a lighthouse optical system designed and built by Vega Industries Ltd. in Porirua, New Zealand. It was originally designed in 1993-95 with the assistance of the United States Coast Guard 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.

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

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Wikipedia