Poul Henningsen developed the PH 5 in 1958 in response to constant changes to the shape and size of incandescent bulbs by bulb manufacturers. The PH 5 Pendant was introduced as a classic new product, and no one knew at the time that it would eventually become synonymous with the PH light. Irrespective 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. Poul Henningsen wanted to improve the colour reproduction characteristics of the light source in the PH 5. Small red and blue shades were therefore inserted to supplement the colour 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 colour. To mark the 50th anniversary of the PH 5 in 2008, the PH50 was introduced – a high-gloss version in five new colours. In 2013 the PH 5 was introduced in 4 new matt colour combinations.