Dynamic Annual Metrics for Contrast in Daylit Architecture Siobhan Rockcastle 1,2 and Marilyne Andersen 1,3 1 MIT, Building Technology Lab 77 Massachusetts Avenue Room 5-418 Cambridge, MA USA 02139 2 Present Address Northeastern University 360 Huntington Ave, 151Ryder Hall Boston, MA USA 02115 s.rockcastle@neu.edu 3 Present Address EPFL, LIPID Laboratory Building BP, Station 16 1015 Lausanne, Switzerland marilyne.andersen@epfl.ch Keywords: Contrast, Dynamic Daylight, Spatial Contrast, Luminance Variability Abstract Daylight is a dynamic source of illumination in architectural space, creating diverse and ephemeral configurations of light and shadow within the built environment. It can generate contrasting levels of brightness between distinct geometries or it can highlight smooth gradients of texture and color within the visual field. Although there are a growing number of studies that seek to define the relationship between brightness, contrast, and lighting quality, the dynamic role of daylight within the visual field is underrepresented by existing metrics. This study proposes a new family of metrics that quantify the magnitude of contrast-based visual effects and time-based variation within daylit space through the use of time- segmented daylight renderings. This paper will introduce two new annual metrics; Annual Spatial Contrast and Annual Luminance Variability. These metrics will be applied to a series of abstract case studies to evaluate their effectiveness in comparing annual contrast-based visual effects. 1. INTRODUCTION Perceptual qualities of daylight, such as contrast and temporal variability, are essential to our appreciation of architectural space. Natural illumination adds depth to complex geometries and infuses otherwise static interior spaces with shifting compositions of light and shadow. Architectural space is greatly altered by the ephemeral qualities of daylight, yet there is a lack of metrics that address these perceptual factors on a dynamic scale. Over the past several decades, there have been significant improvements in our understanding of daylight as a dynamic source of interior illumination. Illuminance- based methods of daylight analysis have developed from static metrics such as Daylight Factor (Moon and Spencer 1942) to annual climate-based metrics such as Daylight Autonomy (Reinhart et al. 2006) and Useful Daylight Illuminance (Nabil & Mardaljevic 2006) to account for a more statistically accurate method of quantifying internal illuminance levels (Mardaljevic et al. 2009). While these annual illuminance-based metrics represent a significant improvement in our understanding of climate-based lighting levels across the year, they still experience many of the same limitations as daylight factor in their static representation of performance through a single surface. (Reinhart et al. 2006). As occupants perceive space from a three-dimensional vantage point, illuminance-based metrics such DA and UDI cannot express the dynamic nature of sunlight from a human perspective. Luminance-based methods of daylight analysis are more appropriate for determining the compositional impacts of contrast as they can evaluate renderings and/or photographs taken from an occupant’s point-of-view (Newsham et al. 2005). Existing luminance-based metrics can be organized into two main categories: those that predict glare-based discomfort due to high ratios of contrast within the visual field, and those that evaluate luminance ratios or ranges to infer human preferences to brightness and composition. Those metrics that quantify luminance-based sources of glare are fragmented among no less than seven established metrics (Kleindienst and Andersen 2009). The most ubiquitous of these metrics, Daylight Glare Probability DGP (Weinhold and Christofferson 2006), establishes that high levels of contrast within our field of view negatively impact visual comfort. Although glare-based metrics are capable of quantifying contrast ratios and anticipating sources of luminance-based discomfort within a perspectival view, they do not provide a method for quantifying the positive aspects of brightness, contrast, or daylight variability.