A simplified method to estimate energy savings of artificial lighting use from daylighting

This paper provides a simplified analysis method to evaluate the potential of daylighting to save energy associated with electric lighting use. Specifically, impacts on daylighting performance are investigated for several combinations of building geometry, window opening size, and glazing type for four geographical locations in the United States. Four building geometries with various window-to-floor areas, along with different glazing types have been analyzed. It was determined that for most commercial buildings with glass transmittance values above 0.5, increasing window area to floor area ratio above 0.5, daylighting does not provide significant additional lighting energy savings. A direct correlation has been established between window transmittance and window area on annual lighting reductions. A model is proposed to estimate lighting energy savings given perimeter area, window area, and window type. Verification and validation of the model's predictions are demonstrated using results from building energy simulation as well as experimental data.