# New Approaches in Dynamic Metrics for Lighting Control Systems: A Critical Review
## 1 Introduction  
### Background  
Over the past few decades, increasing emphasis on energy efficiency and occupant well-being has driven significant innovation in architectural daylighting strategies. One of the most notable outcomes of this shift has been the development of a wide range of daylighting metrics designed to assess the availability and effective use of natural light within buildings. Many of these metrics were developed with the explicit aim of assessing and promoting the effective use of natural daylight in buildings, thereby reducing the reliance on electric lighting as a logical consequence. This has led to their integration into more advanced applications, such as intelligent lighting control systems. A particularly relevant development in this area is the emergence of sensorless control strategies [1], where simulation-based metrics act as predictive inputs for lighting regulation, enabling cost-effective, sensor-free solutions based on architectural and climatic parameters. What follows is a brief overview of the role daylighting plays in architectural design, energy efficiency, and occupant well-being, serving as a foundation for the critical analysis of a selection of daylight metrics--both well-established and emerging--that exemplify the current landscape of tools available for evaluating and guiding daylight-responsive design. Effective daylighting strategies offer significant energy-saving potential [2; 3; 4; 5], reducing reliance on electric lighting [6; 7; 8] and contributing to a building's overall environmental performance. Lighting design in educational spaces is paramount, requiring attention to visual comfort for learning activities [9] and appropriate thermal conditions [10; 11]. Notably, daylight significantly contributes to students' perceptual capacity [12], a relationship closely linked to the configuration of fenestration [13]. While lighting affects visual and thermal comfort [14; 15], its impact extends to non-visual biological processes, particularly the regulation of melatonin, a hormone synthesized by the pineal gland that is strongly modulated by light exposure [16]. The suppression of melatonin by light--particularly short-wavelength (blue) light--quantified as circadian stimulus (CS), is essential for the synchronization of the circadian rhythm, influencing sleep, alertness, and other physiological functions [17]. The human circadian system's reaction to light diverges significantly from that of the visual system. While visual acuity is most responsive to middle-wavelength light, peaking around 555 nm, circadian entrainment, as measured by melatonin suppression, exhibits heightened sensitivity to short-wavelength (blue) light, with a peak near 460 nm [18]. The circadian system is also critically dependent on the timing of light exposure; light before the minimum core body temperature delays the circadian clock, whereas light after advances it. This system exhibits a temporal dependency, requiring minutes of light exposure to elicit a response, contrasting with the milliseconds of visual response. Empirical models, such as the one developed by [PERSON] et al. in 2005 [16], aim to provide a more nuanced understanding of how light influences circadian rhythms. The sensitivity of the circadian system to light is modulated by prior light exposure, with higher daytime exposure reducing nocturnal sensitivity. Daylight, characterized by its optimal spectrum, intensity, duration, and timing, stands as the ideal synchronizing agent for the human circadian system, a role it has fulfilled for millennia. Despite daylight's idealness for synchronizing the human circadian system, in contemporary indoor environments, electric lighting often blurs the distinction between day and night, disrupting natural circadian rhythms and potentially compromising human health. Research has linked circadian disruption to various health issues, including increased morbidity [19], depression [20], and multiple sclerosis [21], with adolescents demonstrating heightened vulnerability [22].