1739, builder unknown, altered 1820 and 1866, originally coal fired.

William Crispe obtained a patent from Trinity House dated 2 June 1737 and he and his partner Benjamin Lund built the tower which is said to have first shown its light on 25 March 1738. The top of tower was rebuilt in 1820 when the lighthouse was taken over by Trinity House and an oil lantern was fitted. In 1839, the lamps were replaced with dioptric apparatus and in 1866 a new lantern was fitted with helical glazing, a new powerful optic and a new iron gallery. This increased the height of the tower to 30/18m (99ft). Sailing Directions dating to 1884 note 'The lighthouse on Flatholm island is a white tower 99 feet high, and from an elevation of 164 feet above high water, is exhibited a white light under occulation twice in quick succession every half-minute:- reappears at full power for three seconds and again suddenly disappearing for three seconds; reappears at full power for the remainder of the half minute; which in clear weather should be visible for a distance of 18 miles. A red sector is shown between the bearings of S by E 3/4 E and SW 1/4 S embracing the space between the Ranie spit buoy and Monkstone beacon.'

Sources include:
Admiralty; 1884, Sailing Directions for the Bristol Channel, 4th Ed, pg125

RCAHMW, September 2014.