range-lights

Century Dictionary and Cyclopedia

1. Two or more lights, generally in lighthouses, so placed that when kept in line a fair course can be made through a channel: where two channels meet, the bringing of two range-lights into line serves to mark lite turning-point into the new channel.
2. Lights placed aboard ship at a considerable horizontal distance from each other, and in the same vertical plane with the keel. They are used to give a better indication of changes of course to approaching vessels than is afforded by the ordinary side and steaming lights.