Direct Sunlight Analysis: A Simplified Approach to Complex Residential Design

Spatial Daylight Autonomy (SDA) and Annual Sunlight Exposure (ASE) are widely adopted metrics for daylight performance assessment in sustainable building design. While valuable, the complexity of these metrics, particularly due to the influence of indirect bounced light, makes them difficult to interpret, especially in high-density residential buildings with multiple apartment units. Additionally, the computational intensity of such analyses limits their practical use in early-stage design or unit comparison. As a result, potential residents often rely solely on direct sunlight exposure when evaluating units without access to meaningful comparative data. To address this gap, this study proposes a simplified daylight evaluation metric, termed the Annual Daylight Index, that is both intuitive and computationally efficient. The index is defined as the total number of annual sunlight hours received across all floor areas of a building, divided by the number of rooms. Implemented using visual programming within a BIM environment, the method leverages a reverse sunlight tracing approach. Its accuracy and efficiency were verified by comparing results and computation times against established daylight simulation tools. The resulting index enables both micro (unit-level) and macro (building-level) comparisons, offering a practical tool for designers, residents, and researchers engaged in daylight evaluation of multi-unit housing projects.