Effects of Urban Obstructions on Spatial Daylight Autonomy (sDA) and Daylight Glare Probability (DGP) in Tropical Mid-rise Housings

The limited research on obstruction-driven daylight reduction continues to hinder efforts to optimize natural daylight in compact mid-rise residential buildings. This study systematically examines how features of nearby obstructions, such as height, surface reflectance, and distance, along with street width, affect indoor daylighting in tropical residences. It employs an integrated approach combining climate-based simulations with occupant perception surveys for validation. Using IES-VE with RadianceIES, climate-based daylight modeling was conducted at the Sri Aksalaya mid-rise apartment complex in Tirupur, India. A total of 1,152 simulation scenarios were performed, varying the room layout orientation (north-east and south-west), road width (4–10 m), obstruction height (G to G+3), and façade reflectance (30–65%). Daylight performance was assessed using two metrics: Spatial Daylight Autonomy (sDA300/50%) and Daylight Glare Probability (DGP). The results were validated through structured surveys of 57 residents across all floors. Findings indicate that external obstructions are the primary factors impacting daylight performance; those located closest to the building (4 m from the building) reduce sDA by up to 67% compared to open conditions. The proximity of obstructions results in insufficient daylight (sDA < 50%) on the lower floors, whereas the upper floors experience excessive glare (DGP > 0.40). The middle floors are most affected by façade reflectivity, with the probability of glare increasing by 250% as reflectance rises from 30% to 65%. Statistical analysis revealed a strong correlation between simulation metrics and occupant satisfaction (R²= 0.84, p < 0.001). Window performance was orientation-dependent; from the selected room layouts, 1, 3, and 4 performed best for north-east, while layouts 2, 3, and 6 were ideal for south-west. Overall, urban morphology greatly influences daylight access and visual comfort in tropical homes. The study highlights the importance of context-specific fenestration design, façade reflectance, and floor-level strategies to optimise daylight and minimise glare in multi-floor residences in tropical settings.