CIE x050-PO097 PDF

There is now an increasing emphasis on reducing the overall level of lighting in towns and villages. The priority is to reduce energy consumption thanks to energy costs and decrease a light pollution in towns, villages and general space. This has an understandable impact not only on road safety but a whole range of other situations. The main objective of this research is to develop an analytical tool to characterize the average brightness levels generated by street public lighting.

Usually measuring tools are working with photopic preferences. The conversion to mesopic vision as defined by CIE norm 191:2010 - RECOMMENDED SYSTEM FOR MESOPIC PHOTOMETRY BASED ON VISUAL PERFORMANCE. Such approach tool should be able to determine the difference in the perception of the visual scene for photopic and mesopic adaptive luminance. The purpose is to test whether, as a matter of economy, street lighting could be dimmed to provide a mesopic pedestrian vision regime while maintaining adequate safety. Possible interferences from bright sources such as advertising boards were tested: in particular their ability to revert the vision mode to photopic, temporarily reducing visual gain and causing some problems with immediate perception. The transition area between the photopic and mesopic thresholds is important for drivers/pedestrians. The conventional threshold is set at 5 cd·m^-2 by the CIE. (CIE, 2010)

For correct visual task, ensure safety in the area the human eye needs enough contrast in mesopic vision at reduced light level.