Harry Claude Lee Cooper trained as a lighthouse engineer in London under the eminent engineer William T. Douglass and became an associate member of the (British) Institution of Mechanical Engineers. He went to Paris, France, in 1900 to study the manufacture of lighthouse equipment and worked on its construction for the Paris Exhibition of 1900. In 1901 Douglass sent him to New South Wales, Australia, where he supervised the building of the lighthouse at Cape Byron. On its completion he came to the Cape Colony in 1902, where he was appointed as an engineering assistant in the Public Works Department on 20 September that year. On 1 July 1906 he was promoted to assistant engineer in the same department, under the chief engineer William Craig*. After the formation of the Union of South Africa in 1910 he was appointed as the country's first lighthouse engineer, a post (from 1916) in the South African Railways and Harbours, with headquarters in Cape Town. He held this position until his retirement in 1941.
From his initial appointment in the Cape Colony to his retirement Cooper was involved in the design, erection and maintenance of lighthouses and the welfare of the staff that manned them. Among others he designed the Cape Hermes lighthouse near Port St Johns (completed in 1904) and the Cape Columbine lighthouse near Paternoster (completed in 1936) and made improvements to the lighthouses at Cape Agulhas, Cape St Blaze, Robben Island, and the Bluff. He was responsible for improvements to the optics and lanterns by introducing vapour petroleum mantle burners and later having them electrified. He was involved in the operation of more than 30 lighthouses and spent about half of each year visiting them by scotch cart to attend to both the structures and their staff. From 1937 he was assisted by the electrical engineer H.G. Jones, who succeeded him in 1941. Long after his retirement the Cooper lighthouse at Durban, commissioned in 1953, was named in his honour.
Cooper became a member of the Cape Society of Civil Engineers (founded in 1902) very soon after his arrival and continued as a member when it was renamed the South African Society of Civil Engineers in November 1909. In 1910 a paper by him on "The lighthouses of Cape Colony" appeared in the society's Minutes of Proceedings (Vol. 8).