Its sweeping beam has guided mariners to safety and cast long flickers of shadow and light across the westernmost edge of the Vineyard for many decades.

But now the Gay Head Light is slated for a lantern change, and in the process the beam will change from sweeping to pulsing.

Lieut. Matthew Stuck of the U.S. Coast Guard aids to navigation branch said recently that the Coast Guard plans to replace the optic rotating light with a flashing LED light sometime in the next few months. The current optic, installed in 1989, is outdated and replacement parts are scarce, Mr. Stuck said.

“Every time something breaks we scavenge from other lighthouses from what remaining bits and pieces are in existence somewhere else,” he said.

The current optic, a rotating back-to-back drum, is 1,000 watts and needs to be replaced about every six months, Mr. Stuck said. The new LED light will be 80 watts and will not need to be replaced for several years.

The new lens will still be colored red, he said.

Not all Aquinnah residents think the change is a sign of progress. At a recent meeting the town selectmen voted to send a letter asking the Coast Guard to hold off on the plan.

One person who attended the meeting was Lenny Butler, who is a member of a town committee developing a plan to relocate the lighthouse due to severe erosion at the Gay Head Cliffs.

“What is important to us is we do not want [the change] to destroy the historic character and nature of that sweeping light,” Mr. Butler told the Gazette later. “To have it replaced with the flashing, cold quality of light from an LED is very disturbing to me and everyone else in town.”

The town has begun steps to take ownership of the lighthouse, following the recent path of Edgartown with its lighthouse. Sometime in the next year the Coast Guard is expected to declare the Gay Head Light surplus property, and under the National Historic Lighthouse Preservation Act the town will be eligible to become the owner. Relocation of the light will follow.

Mr. Stuck said the Coast Guard is “not in a rush” to replace the light but said he thought it would likely happen sometime in the next few months. He acknowledged the nostalgia for the sweeping light, but said a properly functioning optic is critical.

“One never knows with dated equipment . . . We want to make sure we’re giving the mariner the most reliable signal, at the best cost to the public,” he said. “We know there is some sense of disappointment.”