No abstract

Light is the major synchronizer of circadian rhythms to the 24-hour solar day. Compared to the visual system, the circadian system requires more light to be activated and is more sensitive to short-wavelength light. Without access to daylight, or electric lighting providing a comparable amount, spectrum, distribution, duration, and timing, human health and well-being may be compromised. This may be particularly true for those confined indoors, such as patients in hospitals and residents in care facilities. Architectural and design features, including window size, surface reflectances, and furniture placement, impact circadian stimulus levels. This paper details results of simulations used to determine the percentage of days that patients would receive a minimum level of circadian stimulation as a function of different window-to-faç ade ratios, surface reflectances, and latitudes.

A field study was conducted with eighth-grade students to determine the impact of morning light on circadian timing, sleep duration and performance. Before and during school hours for a week in February 2009, half the students studied wore orange glasses that minimized short-wavelength light exposure needed for circadian system stimulation. A control group did not wear the orange glasses. The Daysimeter, a circadian light meter, measured light/dark exposures in both groups for seven days. Circadian timing was significantly delayed for those students who wore orange glasses compared to the control group. Sleep durations were slightly, but not significantly, curtailed in the orange-glasses group. Performance scores on a brief, standardized psychomotor vigilance test and self-reports of well-being were not significantly different between the two groups.

Daylighting systems offer tremendous potential for reducing the energy consumption of electric lighting, but their usage has been inhibited by high costs and imperfect performance of current technologies. This paper presents predictions of energy savings for two proposed daylighting technologies, a daylight-sensing switch and an automatic blinds system, which employ simple, inexpensive components and designs. Assumptions of solar irradiance, blind position, blind operation behaviour, and light switching behaviour were combined with illuminance data and daylight factors to develop an algorithm for calculating the potential energy usages of six different systems in commercial private offices and open plan offices. Results show that the combined usage of the proposed technologies perform with an average annual energy saving of 24% compared with manual switching and blinds operation in Albany, New York. Compared with a photosensor-operated dimming system, the proposed technologies combined show better performance during summer months. Comparisons were also made for the systems in six US climatic regions.

Daylight is a key component of green building; however, no prevailing metric has emerged to help identify buildings that are well-daylit buildings. This paper proposes a 'daylighting dashboard'; a visual representation of a design's potential to meet eight design goals: average illuminance, coverage, diffuse daylight, daylight autonomy, circadian stimulus, glazing area, view and solar heat gain. This metric allows for informed decisions to be made early in the conceptual phase of design, and highlights aspects of design that may need further development, while there is still the opportunity to make modifications. These eight goals should be prioritized as appropriate for individual projects, rating systems or code requirements. This early indication of performance of conceptual design alternatives is likely to guide architects to better daylit buildings.