This paper describes a method to calculate the entropy and exergy associated with architectural daylighting. The purpose for using these concepts is to show explicitly the irreversible energy conversion process of solar radiation incident upon glazing during the course of daylighting, and to provide a global understanding of how a daylighting systemworks. This method has been tested for a room having a single window with single clear or reflective glazing, each under a clear and an overcast sky. The result indicates that the exergy contained in solar radiation admitted by any daylighting system is first consumed by illuminating the requisite room surfaces while the entropy produced is given off as waste. So-called energy-efficient daylighting systems therefore selectively admit solar exerey to meet the illumination requirements.
