Melanopic EDI or m-EDI for short is the circadian metric that has been adopted by the international commission on lighting (CIE). The CIE issued an international standard, CIE S 026:2018 (CIE 2018), that defines a system for studying the measurement of circadian lighting.
Science has identified a specific group of cells in the eye which are responsible for communicating the physiological (non-visual) effects of light to the brain. There is a push within the lighting industry to establish a metric that can be used to measure the circadian impact of light, which will also give designers way to create spaces that provide an appropriate amount of light for the human circadian system. In an attempt to further understand the data, a researcher analyzed 19 different independent circadian lighting studies and in this meta-analysis the researcher concluded that there are two (2) metrics which account for a wide range of physiological effects of light – equivalent melanopic lux (EML) and melanopic EDI (m-EDI). Interestingly, both of these metrics use models with a peak sensitivity to sky blue region of the visible spectrum at 490nm. Another study was performed to evaluate whether the s-cone we use for color vision has an impact on the circadian system and the study revealed that the s-cone did not add anything above the melanopic lux value, further validating the use of EML and/or m-EDI as circadian metrics.
Science is converging on the appropriate metric to use for daytime and nighttime circadian light exposure. Based on the similarities between the EML and m-EDI models, designers can start now using melanopic (m/p) ratios with confidence. Currently, the research is pointing to equivalent melanopic lux or melanopic EDI as the best path forward. In addition the CIE recommends that people receive high melanopic lux during the daytime hours and low melanopic lux or melanopic EDI at night.