"A bird-cage lantern was the style of lantern common to American lighthouses in the early years of the nineteenth century. When Fresnel lenses were introduced to the country in the 1850's, most lighthouses were retrofitted with new lanterns, as the older ones could not support the new style of lens. Consequently, fewer than a dozen lighthouses with original bird-cage lanterns survive in the United States; those that do were discontinued before they could be fitted for the new lantern.

The lanterns received their name because of their appearance; they are shaped like wire bird cages."
- Wipedia