VRB-25

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.

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.

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, using optical sensing of a circular pattern of alternating black and silver lines located around the bottom of the turntable.

The acrylic lenses and cylinder surrounding the whole mechanism are designed to be UV resistant, but still require replacement approximately every five years.

Although the units have been successful in their adoption, there has been occasional controversy (at Egg Rock Light in Maine, for example[8]) when the Coast Guard has removed the lantern from the tower after installing a VRB-25.