In 1874 Ludvig R. Poulsen sets up a wine importing business under the name Kjøbenhavns direkte Vin-Import-Kompagni (The Copenhagen Direct Wine Import Company). The firm closed down in 1878. In 1892 Ludvig Poulsen opened his second business, this time selling tools and electrical supplies. In 1896 Ludvig R. Poulsen hires his nephew, Louis Poulsen. Ludvig R. Poulsen dies in 1906. His nephew Louis takes over the business and, two years later, moves it to Nyhavn 11, which is still the domicile of the company's head office today. Five years later, Sophus Kaastrup-Olsen becomes a partner in the firm, whose name is changed to Louis Poulsen & Co. In 1914 Louis Poulsen & Co. publishes its first catalogue – featuring machines and tools. In 1917, Sophus Kaastrup-Olsen buys Louis Poulsen's share in the firm for 10,000 Danish kroner and becomes the sole owner of Louis Poulsen & Co.
Designer Poul Henningsen begins working together with Louis Poulsen in 1924, with a view to taking part in an international exhibition for decorative art to be held in Paris called "Exposition Internationale des Arts Decoratifs & Industriels Modernes". A competition is held to find qualified participants: Henningsen is one of the winners. Next year, Poul Henningsen's lamps earn Gold medals in this exhibition.
In 1926 Louis Poulsen and Poul Henningsen are awarded a contract to provide lighting for the newly constructed Forum building in Copenhagen using the now-legendary PH lamp with three shades system.
Louis Poulsen starts marketing light fittings, and its first lighting catalogue is published with descriptions in Danish, German, English and French. In 1941, at the time of World War II, Louis Poulsen & Co. A/S acquires the Laurits Henriksen metal goods factory in Copenhagen and becomes a manufacturer of lighting fittings.
Henningsen designs a blackout lamp for the Tivoli Gardens in Copenhagen which allows the Gardens to stay open until midnight: the light from the lamps cannot be seen from aeroplanes flying over the city.
The PH5 lamp is launched in 1958: the 5 in its name refers to its 50 cm diameter.
The first lighting subsidiary outside Denmark is set up in Western Germany in 1962. Other subsidiaries are established in France, in 1964 and in Sweden, 1975. In 1967 the partnership I/S El-Salg is founded. After 2 years Elpefa A/S moves to a new factory building at Sluseholmen and takes over all production and assembly of fixtures and fittings. In 1977 Elpefa A/S merges with Louis Poulsen. Louis Poulsen class B shares are quoted on the Copenhagen Stock Exchange for the first time. 1985, a lighting subsidiary in the United States, a wholesale electrical supplies business in the Faroe Islands, and JO-EL A/S are set up. In 1987 a lighting subsidiary in Norway is established. Louis Poulsen Group sales pass the 1 billion DKK mark. Subsidiaries in Australia and Netherlands are opened the following year. In 1989, Louis Poulsen purchases Skandia Havemann's El A/S, thereby acquiring 16 wholesale electrical supplies outlets.
Poul Henningsen would have turned 100 years old on 9 September 1994. Louis Poulsen & Co. A/S celebrated the occasion by publishing a book on the history of the PH lamp, by recreating the PH table lamp and TREPH pendant of the late 1920s, and by arranging an exhibition of old PH lamps at the Design Museum Danmark (Kunstindustrimuseet) in Copenhagen.