PH designed the three-shade system in 1925-1926 with Louis Poulsen for an exhibition in Paris. He sought to create glare-free, directed light with incandescent bulbs. The family of 30 lights, including three outdoor models, has grown to over 1000 models. Table, floor and wall lamps, chandeliers and countless combinations existed, with various sizes, colours and metal or glass materials to produce warm, cold or diffuse light. By using a logarithmic spiral design, PH achieved even light distribution and reduced glare and shadow. The light codes refer to shade size, with 20 cm top shades and corresponding lower shades. The PH 2/1 Stem Fitting was introduced in 2003 with 20 cm top shades and lower shades from the smaller 1/1 model.