Residents in a Co Down coastal town say they will confront contractors today as they fear one of their oldest landmarks will be taken away under their noses.
A six-ton antique lamp has shone from the lighthouse at St John's Point in Killough for 176 years.
It has brought fishermen to the shore, once guided the Titanic, and found fame in a Van Morrison song.
But officials claim the lamp, which rotates in mercury, is a health hazard. The Commissioners of Irish Lights want to replace the huge bulb with a more energy-efficient LED light.
Outraged residents do not want to see the traditional light replaced and have formed a campaign group opposing any change.
Eileen Peters is concerned the area's cultural and historical significance will be swept away with the modernisation.
She said: "If that were to go, all you would have would be a thing like a bicycle light or an airport landing light. A very ugly LED light at the front of the building, which is a listed building and shouldn't really be desecrated in that way."
Fisherman Ross Mulhall said: "When you're out at sea, it's very cold, dark and lonely and once you can see the light, you know where you are, where home is, you feel a sense of security and it reassures you."
Others have rubbished claims that the change is down to health and safety concerns.
Some residents believe new contractors are starting work today at the site of St John's Point, and they fear changes could be made without a proper consultation process.
Mr Murphy explained: "We've heard they're coming in on Monday to start work on the light, but we can't see how they can, because it's a listed building."
Workers have been at the site since October, carrying out renovations in line with the Lighthouse Tourism Trail, a £2.5m project which promotes maritime safety and hopes to cash in on the tourism industry.
Locals opposed to replacing the beam will gather early today to confront contractors to find out if their wishes have been overridden by the commissioners.
The current Fresno lamp can be seen up to 30 miles away, and is one of only a few left across the world. A more modern replacement would only provide visibility for around two-thirds that distance.
The lighthouse was mentioned in Van Morrison's song Coney Island, in which he describes stopping off at St John's Point.
Shopkeeper William Mulhall explained: "Van Morrison's father had a little house on Coney Island and he would come and stay here."
The building, painted with distinctive yellow and black stripes, is held dear by those living in the coastal community, with the sweeping beam a proud feature of the Down shoreline.
Public meetings have been held in the area with those attending keen to see the lighthouse preserved for future generations.
Local politicians have also backed the campaign. Sinn Fein MLA Colin Hazzard has written to the Commissioners, supporting residents' concerns.
He is urging the lighthouse body to work alongside the community to find a way forward that keeps both the function and heritage of the building.