Situated at the western end of the Channel Islands, rising from a reef on the south west side of the Island of Guernsey, Les Hanois Lighthouse is important in the development of lighthouse engineering, because not only all the stones in each course but also all the courses were dovetailed together to form one solid mass. Various methods of jointing the stones in rock towers have been employed. Smeaton developed the use of granite blocks for rock towers, and he connected them together with metal pins and marble dowels. Alan Stevenson used a similar method in the construction of the Skerryvore Lighthouse, whilst his father, Robert Stevenson, arranged stones of each course in the Bell Rock, so that they formed a series of dovetails. In this manner each course locked together into a solid single unit, and the courses were then pinned together. It was James Douglass who suggested that the stones might be dovetailed together both laterally and vertically. The cement mortar in the joint formed between the faces so locked the dovetails that the stones cannot be separated without being broken. This method was first employed at the Les Hanois Lighthouse, and it became the pattern for all sea rock towers.
A helideck was constructed above the lantern in 1979. Automation work began at the Les Hanois Lighthouse in July 1995 and the station was demanned in January 1996. The station was converted to solar power with panels mounted around the lower part of the helideck support structure.
A new two position lampchanger with 35 watt metal arc lamps was installed within the existing optic, the rotation of which was slowed down changing the character of the light from two white flashes every five seconds to two every 13 seconds. This is to keep the power requirement low enough to allow solarisation and to increase the length of the flash to achieve the required 20 mile range.
The existing air fog signal was replaced by a single directional electric emitter stack installed in a west facing space left in the ring of solar panels around the helideck support structure. The fog signal is controlled by an automatic fog detector.
The lighthouse is now monitored and controlled from Trinity House’s Planning Centre in Harwich, Essex.