ISSUE OF SKY CONDITIONS.

There are a number of ways to interpret the sky for daylighting purposes. For initial design, stationary (static) sky conditions, such as those standardized by the CIE, provide an acceptable representation of the extreme sky conditions. The use of correlations of daylight illuminance and sky luminance with solar information has been found useful in capturing the hourly trends in the sky as driven by the currently available weather hourly tapes. Most success has been found in the correlation of daylight illuminance with solar irradiance, yet moderate success has also been achieved relating the attenuation of the sky with cloud ratio, confirming the validity of this ratio as a measure of cloudiness. Noteworthy progress has been made in approximating the dynamics of the nonstandard, nonperfect sky.