Design Brief: Understanding Daylight Metrics
(0.5 MB PDF file)
The dynamic nature of sunlight poses many challenges when defining the quantity and quality of daylighting that effectively illuminates an interior space. Static and dynamic daylighting metrics have been developed to inform and guide designers. Sustainable building rating systems such as the United States Green Building Council Leadership in Energy and Environmental Design (LEED®) and the Collaborative for High Performance Schools (CHPS) also require some level of quantifying daylighting designs.
For lighting designers and energy consultants, it is important to understand the various daylight terms, calculation methods, and metrics that are used in the rating systems and by the daylighting community. Each has its place for use when analyzing different aspects of a design. Metrics such as Daylight Factor and Single Point in Time are widely used to give a general sense of the daylight quantity in a given space. Less familiar metrics, which include Daylight Saturation Percentage and various Daylight Autonomy hybrids, tend to be more robust, though more calculation intensive. All hold merit for lighting designers to understand and consider.
This Design Brief describes commonly used terms, various methodologies, and daylight metrics. It provides an opportunity for the advanced reader to understand the facets involved in balancing the quantity and quality of daylight entering into a given space. In particular, metrics are compared and a classroom daylighting example is examined. Also, calculation tools that enable designers to effectively evaluate the impact of their daylighting and electric lighting designs are briefly described.