# New Approaches in Dynamic Metrics for Lighting Control Systems: A Critical Review
## 2 Review
### Dynamic Daylighting Metrics for Health and Well-Being
Thirdly, the circadian efficacy of light is dependent on the timing of exposure. Morning exposure to blue-enriched light has a stronger impact compared to later times of day [18]. Consequently, the same illuminance level can yield different circadian stimuli if the spectral composition varies. While the metric's developers have attempted to address these dynamic factors by calculating CSA during early morning hours using an average spectral power distribution (SPD) from studied locations [64], this approach still introduces a degree of uncertainty. Therefore, further research is required to ensure that CSA accurately assesses circadian entrainment. In addition to the circadian stimulus (CS), a more widespread metric for evaluating circadian-effective lighting is the melanopic Equivalent Daylight Illuminance (mEDI), as defined by the International Commission on Illumination in CIE S 026:2018 [71]. mEDI expresses the melanopic impact of a given light source by referencing it to the illuminance produced by a standardized daylight spectrum (D65), thereby offering a biologically relevant, yet easily interpretable, metric. Its standardization and spectral basis have facilitated its adoption in a range of regulatory frameworks and design tools, including the WELL Building Standard, DIN/TS 6760:2022-08, and emerging ISO/CIE 8995-1:2025 norms [72; 73; 74; 75]. Unlike CS, which simulates non-linear melatonin suppression based on intensity, spectrum, timing, and exposure duration, mEDI is a spectrally weighted static illuminance metric, originally conceived for snapshot assessments. It does not model temporal dynamics or circadian phase sensitivity. However, its relatively simple formulation enables efficient integration into simulation workflows, and recent studies have extended its use to hourly or annual analyses using dynamic climate data and radiance-based simulation engines [76; 77]. This trend has significantly increased its utility in daylight-centric lighting design and building performance assessments. While the two approaches are conceptually distinct--mEDI offering a normative spectral benchmark, and CS providing a biologically grounded dynamic model--they are not mutually exclusive. When used together, they can provide complementary insights: mEDI can ensure compliance with regulatory thresholds, while CS can guide personalized or task-specific lighting strategies aligned with human physiological responses. A major limitation of mEDI stems from its static formulation, which may not fully capture the dynamic nature of circadian-effective lighting. It does not incorporate critical temporal variables such as timing, duration, or pattern of exposure, all of which significantly influence circadian responses. Additionally, mEDI assumes spectral constancy during a given exposure, which can be problematic under natural daylight, whose spectral power distribution (SPD) varies with time of day, weather conditions, and solar position. This variability can lead to mismatches between predicted and actual physiological responses. Moreover, although mEDI values can be computed at regular intervals (e.g., hourly) to approximate dynamic behavior, such simulations still treat each timestep independently, lacking the ability to model cumulative or non-linear effects on the circadian system. Lastly, mEDI, by focusing exclusively on spectral content, does not distinguish between light exposures occurring at different times of day, which can result in overestimations or underestimations of circadian impact depending on context. While its simplicity facilitates implementations in performance simulations and building standards, further developments are needed to improve its alignment with biologically dynamic processes such as circadian entrainment. A brief summary and comparison of both metrics are shown in Table 1.