The Nantucket Harbor Range Lights are range lights

Leading lights

Leading lights are a pair of light beacons, used in navigation to indicate a safe passage for vessels entering a shallow or dangerous channel; and may also be used for position fixing. At night, the lights are a form of leading line that can be used for safe navigation...

 which were built in 1908 to guide vessels through the narrow channel to Nantucket Harbor. They replaced an older arrangement, known as Nantucket Range Lights

Nantucket Range Lights

The Nantucket Range Lights formed a range established to guide vessels down the narrow channel into Nantucket Harbor. They were a predecessor to the current Nantucket Harbor Range Lights....

, which became unusable when the current Brant Point Light

Brant Point Light

Brant Point Light is a lighthouse located on Nantucket Island. It was established in 1746, automated in 1965, and is still in operation. The light station was added to the National Register of Historic Places on October 28, 1987. It has the distinction of being the tenth light on the point, in...

 replaced the 1856 Brant Point Light tower.

They display red and white vertical striped daymark

Daymark

A daymark or a day marker is a structure such as a tower constructed on land as an aid to navigation by sailors. While similar in concept to a lighthouse, a daymark does not have a light and so is usually only visible during daylight hours...

s, type KRW, one of the twelve combinations used by the Coast Guard.

It is not known why the official USCG name of the front light, Nantucket Reef Range Front Light includes the word "reef".