This study examines the influence of vegetation on indoor daylight performance in school buildings located in the hot–humid climate of Chennai, India. With increasing urban development leading to the cutting or relocation of trees, their role in modulating interior daylight conditions has become critically relevant but remains underexplored in the literature. Recognizing a significant research gap in this area, this study employed a simulation-based approach using DesignBuilder 7.4 software. A government school in South Chennai, India, was chosen for this study. A total of 208 scenarios were generated by varying the window-to-wall ratio (WWR), facade orientation, floor level, and tree presence. Daylight performance was evaluated using spatial daylight autonomy (sDA), annual sunlight exposure (ASE), and useful daylight illuminance (UDI), based on IES LM-83-12 and LEED v4 standards. Simulation results showed that a 20% window-to-wall ratio (WWR) failed to meet daylight standards, while a 30–40% WWR with shading consistently performed well. Trees significantly improved daylight metrics, like sDA, UDI, and ASE, more so than orientation or floor level. This study urges regulatory mandates for climate-resilient schools, emphasizing fenestration and landscape integration.

Daylight plays a crucial role in enhancing the physical and mental well-being of occupants, particularly students, who spend approximately fourteen years of their early lives in school classrooms. The built environment significantly influences students’ performance, health, and psychological well-being. Although the National Building Code 2016 mandates a minimum illuminance level of 300 lux, this requirement is not mentioned in the compliance report for school affiliations. Hence, lighting is not evaluated scientifically. This study assesses the existing illuminance levels in classrooms through field measurements and computational daylight simulation using Rhinoceros software with the Climate Studio plugin. The research aims to establish quantifiable relationships between key parameters such as window-to-wall ratio, annual sun exposure, spatial daylight autonomy, shading device configuration, and tree location and propose window optimization strategies for different site conditions. Results from field data and simulations establish that trees and window-to-wall ratios significantly impact daylight availability in classrooms. Optimized window-to-wall ratios should be determined for each façade and floor based on specific site conditions. These findings are useful for the architects to make informed decisions in the pre-design stage to provide sustainable design solutions.