# New Approaches in Dynamic Metrics for Lighting Control Systems: A Critical Review
## 2 Review
### Dynamic Daylighting Metrics for Visual Comfort  
Complementary to these dynamic metrics, which focus on achieving adequate illuminance levels for task performance and energy efficiency, there is a set of dynamic metrics that, while based on the same principles, aim to ensure visual comfort by avoiding both excessive illuminance levels (which can cause glare) and insufficient levels (which can lead to visual fatigue)  
The first of these metrics is Useful Daylight Illuminance (UDI), developed by [PERSON] and [PERSON] [53; 54]. UDI complements Daylight Autonomy (DA) by assessing daylight suitability through defined illuminance ranges. It quantifies the time fraction when indoor daylight levels align with occupant visual comfort, specifically between 100 lx and 2000 lx. UDI categorizes illuminance into three thresholds: UDI fell short (UDI-s, <100 lx), UDI achieved (UDI-a, 100-2000 lx), and UDI exceeded (UDI-e, >2000 lx). Like the DA, this approach offers a detailed interpretation of daylight levels based on actual weather data. While DA and UDI both consider the annual occurrence of target illuminance values, UDI extends beyond DA by incorporating an upper threshold, thus accounting for instances of excessive illuminance. Consequently, UDI-a values are typically lower than DA values calculated at the same minimum threshold, such as 300 lx.  
UDI's upper threshold attempts to address excessive illuminance, which can contribute to overheating and glare. However, it does not directly assess glare phenomena. Glare is influenced by factors beyond simple illuminance levels, such as the size and luminance of light sources, and their position relative to the observer [55; 56]. The upper illuminance threshold can serve as a guideline value in the characterization of architecture, but it cannot replace a more comprehensive study of glare using specific metrics such as Unified Glare Rating (UGR) [43; 57] or Daylight Glare Probability (DGP) [58; 59; 60].  
To complement sDA, IES also introduced another visual comfort-oriented dynamic lighting metric: Annual Sunlight Exposure (ASE). This metric quantifies the percentage of an area that receives direct sunlight above a specified direct sunlight illuminance threshold for more than a defined number of hours per year [52]. While sDA serves to indicate whether a minimum level of illuminance is maintained throughout the year in an area, ASE focuses on excessive levels of illuminance due to direct sun, which can result in unwanted glare, discomfort, or excessive heat gain. Being a spatial metric, its strengths and weaknesses are akin to those of sDA. While it offers a clear and actionable estimate for designers, it lacks the granularity offered by other non-spatial metrics. Additionally, ASE suffers from the same shortcomings as UDI's upper threshold. Issues such as glare or discomfort are linked to but not limited to an excessive illuminance value [55; 56; 61]. Therefore, while a high ASE value indicates excessive illuminance within the study area, it does not provide a precise assessment of phenomena such as glare or overheating, for which more specific and better-qualified metrics already exist.