The PH 2/1 wall lamp is part of the PH 3-shade family, and the principle of the PH 3-shade luminaire was realized during the hectic few months of the winter of 1925-26 for a large exhibition hall in Copenhagen, Denmark, called "Forum". This is what Poul Henningsen said about this new luminaire in 1926: "The real innovation of the PH luminaire is that it produces glare-free as well as economical lighting. It is easy enough to create glare-free lighting (indirect light and with a thick shade) if a portion of the light can be wasted, and it is also easy to make luminaires that are very efficient if you ignore the fact that they are very irritating to the eyes (strong specular reflection, etc.), but to make lighting that is both economical and glare-free is an art. Prior to the development of the 3-shade luminaire, Poul Henningsen and Louis Poulsen collaborated on the design of luminaires for the Danish pavilion at the 1925 Paris World Exhibition. When Poul Henningsen designed the lights for the World's Fair, he already had in mind the idea of using the logarithmic spiral as the basis for a new shade structure. The combination of diffuse reflection and logarithmic shade curve also gave Poul Henningsen the opportunity to control the brightness and shade of the luminaire since each shade would equally decrease the amount of light emitted depending on the distance to the bulb. The transitions in brightness between each shade would also appear harmonic. The relative size of the shades and their placement was determined by the need to reduce glare, the placement of the light on the shades and the need for light distribution, based on some remarkably simple principles. From the beginning, it was clear that the design was extremely flexible. Not only was it possible to achieve many different sizes, but also with different lower parts having a white, silver or gold painted surface. These different lower parts could provide different lighting properties. Poul Henningsen imagined that in a restaurant the light should be warm and intimate and therefore a golden surface should be used, unlike in a hospital or dentist's office where the white painted surface should be used. The first fixtures were all made with metal shades, but PH also wanted to develop a variant for the fixture that would show a light distribution curve with less downward lighting. The result was a shade made of opal glass with a sandblasted bottom. The shades allowed 12% of the light to pass through and contribute to the ambient lighting of the room while most of the light was still reflected outward and downward by the matte lower parts of the shades. The same principles that govern matte metal shades governed this new shade material. The PH fixtures were designed as a rational lighting system in which the size of the shade, its material and its surfaces could be mutually combined according to the nature of the project. Each upper shade size has a middle and lower shade set so that the proportions between the shades are approximately 3:2:1. One of the first basic models is the PH 5/5. The first number in the fraction indicates the approximate diameter of the upper shade and the second number indicates that the middle and lower shades were intended for that particular upper shade. This means that the 5/5 has an upper shade with a diameter of 50 cm, a middle shade with a diameter of 31 cm and a lower shade with a diameter of 16.5 cm. This combination was suitable when the fixture was to be hung high, but when the pendants were hung lower, it was advisable to use a combination of a large upper shade and smaller middle and lower shades. This is how the PH 2/1 or 3/2 was born. The PH3-shade system was launched as a suspension solution, but very quickly expanded to other types of lighting for tables, floor lamps, wall lamps and many different chandeliers. The result of using different sizes, materials, surfaces, colors and light sources is the development of more than a thousand variants over the years.