A Critical Comparison of Annual Glare Simulation Methods

Recently, there have been multiple proposals for faster methods to calculate glare metrics, daylight glare proba- bility (DGP) in particular. This is driven simultaneously by the lengthy times required to simulate DGP with a con- ventional image-based approach and accumulating evi- dence from subjective glare evaluation experiments showing that accounting for both the saturation and con- trast in a view improves the accuracy of a glare prediction. While some of these methods have been presented with their own validations, comparisons of accuracy across methods are limited by the differences in tested scenarios and resulting distributions of daylight conditions. This study compares six point-based methods and two zonal estimations for quickly calculating hourly DGP values from three viewpoints with different relationships to the window across a range of scenarios. These include sce- narios with direct and semi-specular transmission and oth- ers with specular and semi-specular reflection. We find that while some of these fast methods closely align with results from a reference simulation, others introduce large and consequential errors.