The eldest son of Robert, he followed in his father’s footsteps, being appointed Engineer in 1843, retiring prematurely on account of illness in 1853. He was responsible for twelve important lighthouses, of which the most famous is the superlative Skerryvore of 1844. He wrote an excellent account of this building and also on illumination, a subject of which he was a master. He made improvements in this field especially in the dioptric system; his apparatus, of this kind at Start Point (England) was the first to be used by Trinity House. Apart from scientific pursuits he had literary and classical tastes which are reflected in some of his designs. Of all the Stevensons, Alan had the most sensitive appreciation of architecture.