The Caldey lighthouse is a small, round, brick-lined limestone tower of 17.07m (56 ft), with walls 0.91m (3ft) thick at the base and 2ft 6in at the top. The light is 64m (210ft) above high-water mark and the structure is flanked by keepers' cottages. The flanking two-storey cottages have a one-storey linking corridor forming a `U'-shaped plan with the lighthouse at the centre of the south side. The hipped-roofed and limewashed cottages have coupled octagonal chimneys and there are enclosed gardens to the north.

Event and Historical Information:
It can be speculated as to whether the adjoining monastic site ever maintained a light to guide medieval vessels engaged in the Irish, French and coastal trades. An application to build the light was made in March 1827 on behalf of traders in Carmarthen Bay. It was engineered and built by Joseph Nelson for Trinity House. It was first lit on 26 January 1829 and cost £4,460. It was intended to help coastal traffic, there being a considerable trade in limestone and coal. In August 1830 vessels in the limestone trade were allowed to commute the charge made of 1d per ton each time the light was passed into an annual payment of £1 15s or 10s according to their tonnage. The present lantern was fitted around the middle of the last century. In this building Nelson projected his window lintels to balance the cills, as he did on the Longstone of 1826. The light consisted of 20 Argand lamps and reflectors when built, but the present helical lantern was fitted later in the nineteenth century. Admiralty Sailing Directions dating to 1884 note that the light was distinguishable for about 20 miles. There is still a lighthouse attendant based on Caldey Island although the cottages are now occupied by a private lessee.

Sources:
Admiralty; 1884, Sailing Directions for the Bristol Channel, 4th Ed, pg75
Hague, D, 1994, Lighthouses of Wales: Their Architecture and Archaeology, pg49-52
Select Committee Report on Lighthouses, 1834, Appendix 25

Maritime Officer, RCAHMW, September 2014.