Poul Henningsen developed the PH 5 in 1958, in response to constant changes to the shape and size of incandescent bulbs. At the introduction of the PH 5, Henningsen wrote the following: After 33 years of basically Christian behavior, I have converted to Islam in my relationship to the manufacture of incandescent bulbs. For a generation I have believed that consideration for the consumer and common sense would prevail, but now I have become a fatalist. I have accepted fate, and with Louis Poulsen’s permission, I have designed a PH fixture which can be used with any kind of light source, including, Christmas lights and 100 W metal-filament bulbs (although a fluorescent tube would be too much to ask in the existing form). The PH 5 was introduced as a classic new product and no one knew at the time that it would eventually become synonymous with the PH brand. Regardless of how the light is installed or the light source used, the PH 5 is and remains completely glare-free. The fixture was christened pH 5 due to the 50 cm diameter of the main shade. Henningsen wanted to improve the color reproduction characteristics of the light source in the PH 5. Small red and blue shades were therefore inserted to supplement the color in the part of the spectrum where the eye is least sensitive: the red and blue areas, thereby subduing the light in the middle yellow-green region where the eye is most sensitive. The PH 5 design has been regularly updated as light sources have developed. The PH 5 plus, designed for use with energy-saving bulbs, was introduced in 1994. To achieve higher efficiency, the metal plate was replaced with frosted glass and the light was painted using a purer white color. To mark the 50th anniversary of the PH 5 in 2008, the PH50 (a high-gloss version in five new colors) was introduced.