Evaluating a New Suite of Luminance-Based Design Metrics for Predicting Human Visual Comfort in Offices with Daylight

ABSTRACT

A new suite of visual comfort metrics is proposed and evaluated for their ability to explain the variability in subjective human responses in a mock private office environment with daylight. Participants (n = 48) rated visual comfort and preference factors, including 1488 discreet appraisals, and these subjective results were correlated against more than 2000 unique luminance-based metrics that were captured using high dynamic range photography techniques. Importantly, luminance-based metrics were more capable than illuminance-based metrics for fitting the range of human subjective responses to data from visual preference questionnaire items. No metrics based upon the entire scene ranked in the top 20 squared correlation coefficients, nor did any based upon illuminance or irradiance data, nor did any of the studied glare indices, luminance ratios, or contrast ratios. The standard deviation of window luminance was the metric that best fit human subjective responses to visual preference on seven of 12 questionnaire items (with r² = 0.43). Luminance metrics calculated using the horizontal 40° band (a scene-independent mask) and the window area (a scene-dependent mask) represented the majority of the top 20 squared correlation coefficients for almost all subjective visual preference questionnaire items. The strongest multiple regression model was for the semantic differential rating (too dim–too bright) of the window wall (_adjR² = 0.49) and was built upon three variables; standard deviation of window luminance, the 50th percentile luminance value from the lower view window, and mean luminance of the 40° horizontal band.

KEYWORDS:

• controls
• daylighting
• discomfort glare
• visual perception

ACKNOWLEDGMENTS

Special thanks are due to Dr. Judith Heerwagen, Dr. Peter Johnson, and Professor Joel Loveland. We express our gratitude to University of Idaho Integrated Design Lab staff Brad Acker, Julia Day, Alen Mahic, and Dr. Ery Djunaedy for their assistance.

FUNDING

This work was conducted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Built Environment at the University of Washington and as a research project at the University of Idaho Integrated Design Lab. In these capacities the following organizations provided financial support for aspects of this project. The University of Washington PhD in the Built Environment Program through fellowships, the Nuckolls Fund for Educational Lighting through the Edison Price Fellowship, the Illuminating Engineering Society of North America, specifically the New York City Section’s support through the Richard Kelly Grant and the Golden Gate Section’s support through the Robert E. Thunen Memorial Scholarship, the International Association of Lighting Designers through the Lighting Design Alliance Scholarship, the Northwest Energy Efficiency Alliance and Idaho Power Company through support of technology demonstrations, Construction Specialties, and Warema International for partial product donations.

Additional information

Funding

This work was conducted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Built Environment at the University of Washington and as a research project at the University of Idaho Integrated Design Lab. In these capacities the following organizations provided financial support for aspects of this project. The University of Washington PhD in the Built Environment Program through fellowships, the Nuckolls Fund for Educational Lighting through the Edison Price Fellowship, the Illuminating Engineering Society of North America, specifically the New York City Section’s support through the Richard Kelly Grant and the Golden Gate Section’s support through the Robert E. Thunen Memorial Scholarship, the International Association of Lighting Designers through the Lighting Design Alliance Scholarship, the Northwest Energy Efficiency Alliance and Idaho Power Company through support of technology demonstrations, Construction Specialties, and Warema International for partial product donations.