Horizontal Light Pipe System for Daylight Optimization in Deep-Plan Library Spaces in a Tropical Climate

Deep-plan spaces, such as a library reading area, typically suffer from poor daylight penetration to the core, which reduces visual comfort and increases dependence on artificial lighting. Horizontal Light Pipes (HLPs) are passive daylighting systems that capture daylight through an inlet, transport it through a reflective pipe, and distribute it into the interior. This research examines the performance of HLPs in the second-floor reading room of a university’s Central Library, a typical institutional building in a tropical climate. Field measurements of illuminance were conducted to document existing conditions and later used to validate ClimateStudio simulation results. A Rhino and Grasshopper parametric workflow defined six HLP geometry variables and generated different HLP configurations for ClimateStudio analysis. Multi-objective optimization was performed using the Octopus plug-in to identify the most effective solutions, evaluating 1,100 genomes. Data export and organization were managed through the TT toolbox, and results were analyzed using statistical methods and cross-checked with Design Explorer. Performance was evaluated using daylighting and energy metrics such as mean illuminance, spatial daylight autonomy (sDA300/50%), annual sunlight exposure (ASE1000,250h), and energy use intensity (EUI). Compared with the base case with mean illuminance 393 lux, sDA300/50% of 38.4%, ASE1000,250h of 3.4%, EUI of 83.17 kWh/(m2y), HLP integrated optimized models achieved mean illuminance 760~880 lux with sDA300/50% of 77.33~80.12%, ASE1000,250h of 0.62~0.93% and EUI 71.02~71.13 kWh/(m2y), showing significant improvement over the base case. These results suggest that HLPs can provide better daylight distribution and reduce energy usage in deep-plan libraries. According to the study, HLPs have the potential to be a practical strategy for improving daylight performance in tropical academic buildings.