Light categories

The lights used as aids to navigation are divided into two main categories: the major lights and the minor lights. The major lights are subdivided into two groups: the primary major lights and the secondary major lights.
The primary major lights are of very high intensity, long range, and used for landfalls, coastal passages and key navigational points.
They are placed in lighthouses, lightships and light towers.
The secondary major lights are of high intensity, of shorter range, and they are placed in harbors, river entrances, and along seacoasts.
The minor lights are of low to moderate intensity, placed within harbors, along channels and rivers and are often used to mark isolated dangers.