A rare and valuable lighthouse lens that shone for 120 years in Cape Elizabeth is going to be displayed permanently at the Maine Maritime Museum in Bath. The 1,800-pound Fresnel lens that operated from 1874 to 1994 will be delivered to Bath this week. After the lens was removed and replaced with a modern light, it was displayed for 18 years in Town Hall. The Portland Press Herald reported the town paid $2,500 a year to insure the lens, which is valued at $2.5 million. In April, the town decided to return the light to the Coast Guard because preserving it would have been too expensive. It was going to be shipped to a Boston warehouse before the museum offered to give it a permanent home.