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 a passive daylighting system that captures daylight through an inlet and transports it through a reflective pipe before distributing 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 carried out to record existing conditions and were 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.