Height of Light

The vertical distance from the water’s surface at Mean High Water Springs to the focal plane of a lighthouse’s light source.

Height of Light is a useful measurement in maritime navigation, as it determines the distance at which a lighthouse’s light can be seen by vessels at sea. This measurement is taken from Mean High Water Springs to the focal plane of the light, which is the point where the light beam is emitted. The height is expressed in metres or feet and is a key factor in ensuring that the light is visible over the curvature of the Earth and any intervening obstacles, such as cliffs or headlands.

The concept of “Height of Light” is particularly significant because it directly affects the lighthouse’s visibility range. A higher light can be seen from a greater distance, assuming clear weather conditions and no obstructions. Mariners use this information, often found on nautical charts or in light lists, to calculate their position relative to the lighthouse. It is important to note that the Height of Light differs from the Range of Light, which refers to the maximum distance the light is visible under specific atmospheric conditions. 

In practice, constructing a lighthouse considers the Height of Light to ensure optimal visibility for ships navigating the area. For example, a lighthouse built on a high cliff may have a lower tower, as the natural elevation contributes to the overall height. In contrast, a lighthouse on flat terrain may require a taller structure to achieve the necessary visibility range.