Mesopic Photometry

Mesopic photometry establishes a new foundation for the development of light sources. It enables optimising the luminous flux of light sources in terms of both seeing and energy efficiency. 

Traditionally lighting measures have relied on the international photopic spectral response curve, which was published already in 1924. However, when light levels lower into the mesopic level, the sensitivity of the human eye changes. The mesopic light levels are between daylight and dusk. A new paper by the CIE (International Commission on Illumination) provides an international foundation for measuring low lighting levels. An ISO/CIE standard is on the way. 

Applying mesopic photometry into street lighting improves energy efficiency and traffic safety, as the provided light is amended to suit eye sensitivity better. Globally we are talking about vast savings. The results indicate that with lower lighting levels the sensitivity of the eye turns towards blue. This will affect street and road lighting in the future. It can be assumed that yellow lights will be replaced by blue, which will also render the colours better. Mesopic photometry also prefers white light. Using mesopic photometry already today in lighting design improves energy efficiency and street safety.

Downloadable paper on mesopic photometry (PDF, in Finnish) by the lighting unit of the Aalto University  (Source: Aalto University)