Prospective evaluation of the Circadian Efficacy of (Day)Light in Rooms

Recent studies have attempted to link environmental cues, such as lighting, with human performance and health, and initial findings seem to indicate a positive correlation between the two. Light is the major environmental time cue that resets the human circadian pacemaker, an endogenous clock in the hypothalamus that controls the timing of many 24-hour rhythms in physiology and behavior. Insufficient or inappropriate light exposure can disrupt normal circadian rhythms which may result in adverse consequences for human performance, health and safety. This paper addresses the problem of prospective analysis of building architecture for circadian stimulus potential based on the state of the art in photobiology. Three variables were considered in this analysis: lighting intensity, timing, and spectrum. Intensity is a standard design tool frequently used in illuminating engineering. Timing and spectrum are not commonplace considerations, so the analysis that follows proposes tools to quantitatively address these additional requirements. Outcomes of photobiology research were used in this paper to define threshold values for illumination in terms of spectrum, intensity, and timing of light at the human eye, and were translated into goals for simulation – and ultimately for building design. In particular, the climate-based Daylight Autonomy (DA) metric was chosen to simulate the probabilistic and temporal potential of daylight for human health needs. The developed method was applied to study the impact of key architectural decisions on achieving prescribed stimulus of the circadian system in a hospital patient room design; studied variables included orientation, window size, and glazing material. A healthcare setting was specifically chosen with the intent of follow-on research to validate our findings with actual patient outcome data.