Aligning two fixed points on land provides a navigator with a line of position called a range in the U.S. and a transit in Britain. Ranges can be used to precisely align a vessel within a narrow channel such as in a river. With landmarks of a range illuminated with a set of fixed lighthouses, nighttime navigation is possible.
Such paired lighthouses are called range lights in the U.S. and leading lights in the United Kingdom. The closer light is referred to as the beacon or front range; the furthest away is called the rear range. The rear range light is almost always taller than the front.
When the vessel is on the correct course, the two lights line up vertically. But when the observer is out of position, the difference in alignment indicates the proper direction of travel to correct the course.
1910 construction of two range lights to aid inshore navigation of ships approaching Port McNicoll. With the development of the CPR harbour facitilites and elevator at Port McNicoll in 1912 maritime traffice increased in the area. Lamps originally kerosene. In 1951 electric lamps were substituted. Tay Township funded restoration of the light in the amount of $60,000.
– information from article by Lynda Hook in the January 2012 issue of CHOnews, quarterly publication of Community Heritage Ontario