[1] The Eeragh Lighthouse which marks the North Sound entrance to the bay on the north-western side of the islands, was also constructed at the same time.

The Inisheer Lighthouse had a first order optic, supplied by Chance Brothers of Birmingham that emitted a fixed white light with a red sector signalling the Finnis reef.

[1][5] The optic is located at a height of 34 metres (112 ft), within a lantern room at the top of a limestone tower which has been painted white with a broad central black band.

The two keeper's houses are built close by, but the light is now maintained by an attendant living some distance away, who monitors the equipment via a radio link.

[1] In addition, the lighthouse is equipped with a radar or RACON beacon that emits the letter K in Morse code with a range of 13 nautical miles.