We derive an equation for zenith luminance as a function of turbidity and solar altitude based on analysis of large quantities of luminance and illuminance data measured in San Francisco, California, between September 1979 and August 1982. Using only average turbidity values to predict hourly zenith luminance as a function of solar altitude can produce large errors. We compare the equation derived from our data, which is valid over a wide range of turbidity and solar altitude, to other published models. We also compare the relationship between horizontal illuminance and zenith luminance from the clear sky and conclude that, when ideal clear days are compared, this relationship is similar to earlier work based on measurements in European climates. Finally, we compare our sky luminance distribution measurements to previous published luminance distributions using the diffusion indicatrix. Our results are intended to help improve daylight availability prediction techniques and define additional requirements for data collection.
BT - Energy and Buildings C1 -Windows and Daylighting Group
C2 - LBL-15622 CN - LBL-15622 LA - eng M1 - 3 N2 -We derive an equation for zenith luminance as a function of turbidity and solar altitude based on analysis of large quantities of luminance and illuminance data measured in San Francisco, California, between September 1979 and August 1982. Using only average turbidity values to predict hourly zenith luminance as a function of solar altitude can produce large errors. We compare the equation derived from our data, which is valid over a wide range of turbidity and solar altitude, to other published models. We also compare the relationship between horizontal illuminance and zenith luminance from the clear sky and conclude that, when ideal clear days are compared, this relationship is similar to earlier work based on measurements in European climates. Finally, we compare our sky luminance distribution measurements to previous published luminance distributions using the diffusion indicatrix. Our results are intended to help improve daylight availability prediction techniques and define additional requirements for data collection.
PY - 1983 SP - 283 EP - 291 T2 - Energy and Buildings TI - Zenith Luminance for Daylighting Calculations VL - 6 ER -