Melanopic Equivalent Daylight Illuminance


Aug 26, 2020 | 2 comments

Image Credit:wikimedia


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.


Key Takeaway

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.





  1. Rohan Nagare

    Dear Robert Soler,

    I agree that melanopsin-based ipRGCs are the primary conduits for mediating non-visual effects of lights, however, rods and cones also contribute to these responses via the ipRGCs.

    More importantly, m-EDI is not the circadian metric adopted by CIE S 026. CIE S 026 describes a tool to quantify alpha-opic irradiances and illuminances for all five photoreceptors. Here is an excerpt from the CIE S026 technical note page itself –

    “there is no single action spectrum for non-visual responses. The actual NIF effects due to ocular exposure to light depend on the combined responses of all photoreceptors and there is good evidence for the potential for all receptor types to contribute to these responses”

    Here is the link to the CIE description of S 026 –

    Best regards,

  2. Andrew Guido

    Thanks Robert for an easy to read blog post explaining melanopic lux and melanopic EDI as metrics to help understand the book ends of circadian impact of light on human biology. I am developing a unique “healthy home” under my brand called “ERTH” in Toronto in Canada. In this first generation new home we are addressing optimized air, water, light and sound and with potentially reduced EMF and EMR exposure. Would be very interesting in exploring using Bios lighting. We are in the process of establishing a strategic alliance with a University that will use the home that we recently acquired in the city that will be knockdown and rebuilt as a “living lab”. I can be reached at or on my mobile at 1-416-526-3909.


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