THE ROLE OF DAYLIGHTING IN LEEDTM CERTIFICATION : A COMPARATIVE EVALUATION OF DOCUMENTATION METHODS

In this paper, the LEED Daylighting Credit (IEQ 8.1) is examined with reference to currently accepted calculation techniques in daylighting. A review of the derivation and use of the Daylight Factor requirement reveals that the LEED use of the metric is not well defined or constrained to the useful scientific understanding of the term. The Apple Flagship Store in Los Angeles, California, is used to develop a comparative example for four compliance documentation procedures. The quantitative daylight factor results from the LEED spreadsheet calculations are presented in detail and compared with results from a RADIANCE computer simulation, physical model testing in a calibrated mirror box sky, and on-site measurements. The conclusions firmly indicate that the LEED spreadsheet method significantly over-predicts the levels of daylight due to problematic modifications in the Daylight Factor rules of thumb developed by R.G. Hopkinson. The RADIANCE and physical models are both in line with expected levels and distributions of daylight intensity, while the on-site measurements are similar to the software and physical model simulations, but skewed by changing exterior sky conditions.