The PH 3½-2½ Glass Table lamp was designed in 1928 and is one of many advanced projects undertaken by Poul Henningsen in the development of his world-famous three-shade system from 1926.

Poul Henningsen devoted most of his life to taming electric light. He based his three-shade design on a logarithmic spiral to make optimum use of the light source. He was constantly doing calculations and tests. The form of the shades was determined by the way they were required to shape and reflect the light, and the lamp was designed to be glare-free.