The light tower Sumburgh Head Lighthouse is still an operational marine navigation aid, maintained by the Northern Lighthouse Board. It is the oldest Stevenson lighthouse in Shetland and has been in continuous use since its construction in 1821.
The light shone for the first time on 15th January that year; a single stationary light fuelled by oil. In 1868, paraffin replaced oil as the fuel for the light and this continued all the way up to 1976 when electricity was introduced, making the operation much safer altogether.
It has been recognised that even with modern equipment it is almost impossible to better the light projection given by a Fresnel lens. Developed by Inside the lens Augustin-Jean Fresnel, physicist and French Lighthouse Commissioner, the Fresnel lens gathers all available light and bends it into the centre, or bullseye, from where it is projected in a straight line out to sea. To achieve this, the centre of the light source must be very accurately positioned inside the lens. While there have been very few changes to the design of the Fresnel lens, some improvements were made by various members of the Stevenson dynasty. For example, the Sumburgh Head lens has 26 reflectors, rather than the normal 21 of other standard lenses.
The light must continue to rotate without stopping, as the effect of the giant lens is similar to that of a magnifying glass - in this particular case, a magnifying glass that stands eight feet and six inches in diameter. The focal length, which is the distance from the light source to the lens, is three feet. This is known as a first order lens and is the largest standard size deployed in Scottish lighthouses.
The existing rotating light mechanism was installed in 1914, whereupon the 'character' of the Sumburgh Head light was established. Every light has its own character which allows mariners to identify it. Sumburgh Head shows three white flashes every 30 seconds as the three tonne mechanism rotates perpetually on a 200kg bath of mercury throwing its light 23 miles out to sea.
The light became automated in 1991 when Lighthouse Keepers left Sumburgh Head.
Visit the Engine Room to find out about the full history of the Light Tower and the changing technology which has kept mariners safe around the shores of Sumburgh Head for nearly 200 years.