Experimental validation of adaptation coefficient computation in mesopic photometry using LED lighting

Mesopic photometry is the study of visual perception under lighting conditions that lie between bright (photopic) and dark (scotopic) environments, where both cones and rods in the human eye are active. It is particularly relevant for nighttime or low-light scenarios, such as street lighting, where standard photopic measurements may not accurately reflect human visual performance. The CIE MES2 system provides a framework to estimate the adaptation coefficient for mesopic lighting systems by utilizing a fixed-point iteration method. This paper provides an experimental confirmation of the computation method to verify and compare the various methods of iteration by employing a Xiaomi lamp as the light source in a dark room environment. The results agree with the Newton-Bisection method being the best method to estimate the value of the adaptation coefficient, and also highlight the comparability of the CIE recommended fixed-point method for a practical light source.