Irish Lights, along with the other lighthouse authorities around the world, have used mercury to rotate large revolving Fresnel lenses in lighthouse applications since the late 1800s. The system provided a near frictionless environment for the rotation of these large lenses. Mercury is a toxic substance and, despite the many years of reliable service, there is increasing European and International legislation restricting its use, storage and transport. While there is no immediate statutory requirement to remove mercury from lighthouses, it has been Irish Lights’ policy for a number of years that where major re-engineering capital projects are being carried out at lighthouses, the opportunity is taken to remove mercury from these installations. There is no other liquid medium currently available to replace mercury. Accordingly, alternative solutions are designed on a station by station basis to provide the required visual Aid to Navigation.

Irish Lights undertook a project to trial a mechanical slew bearing solution using a redundant lens at Tory Island lighthouse, commencing in 2015. The lens at this lighthouse is a biform (two-tier) hyper-radial lens, one of the largest in service. The trial was carried out over a number of years to ensure reliable operation of the bearing solution. The success of this trial led to the re-establishment of the light utilising the existing Fresnel lens with a low powered LED light source installed within the existing lens in 2019.

Over the next 6 years, Irish Lights will be carrying out engineering upgrade works to a number of high profile land or island d stations, most of which are designated as Listed Buildings in Northern Ireland or Protected Structures in the Republic of Ireland.

A key ive of these works is the retention of the rotating Fresnel lenses which Irish Lights recognise as important to the heritage of the stations and the local areas.